U.S. patent application number 14/003247 was filed with the patent office on 2014-03-06 for method and device for communicating device-to-device.
This patent application is currently assigned to LG ELECTRONICS INC.. The applicant listed for this patent is Byounghoon Kim, Daewon Lee, Hanbyul Seo. Invention is credited to Byounghoon Kim, Daewon Lee, Hanbyul Seo.
Application Number | 20140064203 14/003247 |
Document ID | / |
Family ID | 46879862 |
Filed Date | 2014-03-06 |
United States Patent
Application |
20140064203 |
Kind Code |
A1 |
Seo; Hanbyul ; et
al. |
March 6, 2014 |
METHOD AND DEVICE FOR COMMUNICATING DEVICE-TO-DEVICE
Abstract
The present invention relates to a wireless communication
system, and more specifically, to a method and a device for
communicating device-to-device. The method for a first device to
transmit a signal to a second device according to one embodiment of
the present invention enables the first device to request to a base
station a resource allocation for transmitting the signal to the
second device, receive from the base station scheduling information
for transmitting the signal to the second device, and the signal
can be transmitted from the first device to the second device on
the basis of the scheduling information, wherein the scheduling
information includes information on an uplink resource for
transmitting the signal from the first device to the second
device.
Inventors: |
Seo; Hanbyul; (Anyang-si,
KR) ; Lee; Daewon; (Anyang-si, KR) ; Kim;
Byounghoon; (Anyang-si, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Seo; Hanbyul
Lee; Daewon
Kim; Byounghoon |
Anyang-si
Anyang-si
Anyang-si |
|
KR
KR
KR |
|
|
Assignee: |
LG ELECTRONICS INC.
Seoul
KR
|
Family ID: |
46879862 |
Appl. No.: |
14/003247 |
Filed: |
March 15, 2012 |
PCT Filed: |
March 15, 2012 |
PCT NO: |
PCT/KR12/01891 |
371 Date: |
November 20, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61453967 |
Mar 18, 2011 |
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61475642 |
Apr 14, 2011 |
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61537039 |
Sep 20, 2011 |
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Current U.S.
Class: |
370/329 |
Current CPC
Class: |
H04L 1/1854 20130101;
H04W 28/06 20130101; H04W 72/042 20130101; H04W 74/0833 20130101;
H04W 72/0406 20130101; H04W 92/18 20130101; H04W 72/1289 20130101;
H04W 72/0413 20130101; H04L 1/1861 20130101 |
Class at
Publication: |
370/329 |
International
Class: |
H04W 72/04 20060101
H04W072/04 |
Claims
1. A method for a first UE to transmit a signal to a second UE, the
method comprising: requesting that an eNB perform resource
allocation for signal transmission to the second UE; receiving
scheduling information for signal transmission to the second UE
from the eNB; and transmitting a signal to the second UE on the
basis of the scheduling information, wherein the scheduling
information includes information on an uplink resource for signal
transmission from the first UE to the second UE.
2. The method according to claim 1, further comprising transmitting
a signal for channel state measurement in the second UE.
3. The method according to claim 1, wherein one or more of a
physical uplink control channel (PUCCH), a physical uplink shared
channel (PUSCH), an uplink modulation reference signal (UL DMRS), a
sounding reference signal (SRS) and a physical random access
channel (PRACH) preamble is transmitted on the uplink resource from
the first UE to the second UE.
4. The method according to claim 1, wherein one or more of a
physical downlink control channel (PDCCH), a physical downlink
shared channel (PDSCH), a cell-specific reference signal and a
channel state information-reference signal (CSI-RS) is transmitted
on the uplink resource from the first UE to the second UE.
5. The method according to claim 1, wherein the requesting of
resource allocation comprises: transmitting a scheduling request or
a PRACH preamble from the first UE to the eNB; receiving an uplink
grant from the eNB; and transmitting additional information
including one or more of the ID of the first UE, the ID of the
second UE and a buffer state report of the first UE to the eNB
using the uplink grant.
6. A method for a second UE to receive a signal from a first UE,
the method comprising: receiving scheduling information for signal
transmission from the first UE to the second UE from an eNB; and
receiving a signal from the first UE on the basis of the scheduling
information, wherein the scheduling information includes
information on an uplink resource used for the second UE to receive
a signal from the first UE.
7. The method according to claim 6, further comprising transmitting
ACK/NACK information for the signal received from the first UE to
the eNB.
8. The method according to claim 7, wherein the ACK/NACK
information for the signal received from the first UE is
transmitted to the eNB along with ACK/NACK information for a signal
received from the eNB.
9. The method according to claim 7, wherein ACK/NACK information
for a maximum of N signals received by the second UE is transmitted
on a single uplink subframe, wherein N is a fixed value in both a
case in which the ACK/NACK information for the signal received from
the first UE is transmitted in the single uplink subframe and a
case in which the ACK/NACK information for the signal received from
the first UE is not transmitted in the single uplink subframe.
10. The method according to claim 7, wherein, when the signal from
the first UE is received in a subframe n, the ACK/NACK information
for the signal received from the first UE is transmitted in a
subframe in which ACK/NACK information for downlink data from the
eNB is transmitted when the downlink data is received from the eNB
in the subframe n, an initial uplink subframe from among subframes
after a predetermined process time from the subframe n, or an
initial subframe scheduled to transmit uplink data from among
subframes after a predetermined process time from the subframe
n.
11. The method according to claim 6, further comprising: receiving
from the first UE a signal for measuring the state of a channel
from the first UE; and transmitting channel state information to
the eNB.
12. The method according to claim 11, wherein, when the channel
state information is transmitted in a subframe n, a channel state
information reference resource is set to a latest uplink subframe
belonging to the same uplink HARQ process as that to which the
subframe n belongs from among subframes prior to the subframe n, a
latest uplink subframe from among subframes a predetermined process
time in advance of the subframe n, a latest uplink subframe from
among subframes a predetermined process time in advance of the
subframe n and after a subframe in which control information for
requesting transmission of the channel state information is
received, or a latest subframe scheduled to transmit the signal for
measuring the state of the channel from the first UE from among
subframes a predetermined process time in advance of the subframe
n.
13. The method according to claim 6, wherein, when uplink
transmission of the second UE is set in the uplink resource, uplink
transmission of the second UE is dropped.
14. A method for an eNB to support signal transmission from a first
UE to a second UE, the method comprising: receiving from the first
UE a resource allocation request for signal transmission from the
first UE to the second UE; and transmitting to the first UE and the
second UE scheduling information for signal transmission from the
first UE to the second UE, wherein the scheduling information
includes information on an uplink resource used for the first UE to
transmit a signal to the second UE.
15. A transceiver for transmitting a signal to another device,
comprising: a transmission module for transmitting signals to an
eNB and the other device; a reception module for receiving a signal
from the eNB; and a processor for controlling the transceiver
including the transmission module and the reception module, wherein
the processor is configured to request the eNB to allocate a
resource for signal transmission to the other device, to receive
scheduling information for signal transmission to the other device
from the eNB and to transmit a signal to the other device on the
basis of the scheduling information, wherein the scheduling
information includes information on an uplink resource used for the
transceiver to transmit a signal to the other device.
16. A transceiver for receiving a signal from another device,
comprising: a transmission module for transmitting a signal to an
eNB; a reception module for receiving signals from the eNB and the
other device; and a processor for controlling the transceiver
including the transmission module and the reception module, wherein
the processor is configured to receive from the eNB scheduling
information for signal transmission from the other device to the
transceiver and to receive a signal from the other device on the
basis of the scheduling information, wherein the scheduling
information includes information on an uplink resource used for the
transceiver to receive a signal from the other device.
17. An eNB device supporting signal transmission from a first
transceiver to a second transceiver, comprising: a transmission
module for transmitting signals to the first and second
transceivers; a reception module for receiving signals from the
first and second transceivers; and a processor for controlling the
eNB device including the transmission module and the reception
module, wherein the processor is configured to receive, from the
first transceiver, a resource allocation request for signal
transmission from the first transceiver to the second transceiver
and to transmit to the first and second transceivers scheduling
information for signal transmission from the first transceiver to
the second transceiver, wherein the scheduling information includes
information on an uplink resource used for the first transceiver to
transmit a signal to the second transceiver.
Description
TECHNICAL FIELD
[0001] The present invention relates to a wireless communication
system, and more specifically, to a method and device for
device-to-device communication.
BACKGROUND ART
[0002] Device-to-Device (D2D) communication is a communication
scheme for directly transmitting/receiving data between user
equipments (UEs) without an evolved NodeB (eNB) by establishing a
direct link between UEs. D2D communication may include UE-to-UE and
peer-to-peer communication schemes. In addition, D2D communication
is applicable to machine-to-machine communication, machine type
communication (MTC), etc.
[0003] D2D communication is a method considered for reducing the
burden of an eNB due to rapidly increasing data traffic. For
example, D2D communication can decrease network overload because
data is directly exchanged between devices without an eNB, unlike a
conventional wireless communication system.
[0004] Furthermore, D2D communication can reduce the number of
processes of an eNB and power consumption of devices participating
in D2D communication, increase data throughput and network
capacity, distribute loads, extend cell coverage, etc.
DISCLOSURE
Technical Problem
[0005] An object of the present invention devised to solve the
problem lies in a method for performing D2D communication
efficiently and correctly. Another object of the present invention
is to provide a new D2D communication method for allocating
resources for D2D communication by a network. Another object of the
present invention is to provide a method for efficiently performing
D2D communication request, D2D link detection, allocation of
resources for D2D communication and D2D communication
maintenance.
[0006] The technical problems solved by the present invention are
not limited to the above technical problems and those skilled in
the art may understand other technical problems from the following
description.
TECHNICAL SOLUTION
[0007] The object of the present invention can be achieved by
providing a method for a first UE to transmit a signal to a second
UE, the method including: requesting that an eNB perform resource
allocation for signal transmission to the second UE; receiving
scheduling information for signal transmission to the second UE
from the eNB; and transmitting a signal to the second UE on the
basis of the scheduling information. The scheduling information may
include information on an uplink resource for signal transmission
from the first UE to the second UE.
[0008] In another aspect of the present invention, provided herein
is a method for a second UE to receive a signal from a first UE,
the method including: receiving scheduling information for signal
transmission from the first UE to the second UE from an eNB; and
receiving a signal from the first UE on the basis of the scheduling
information. The scheduling information may include information on
an uplink resource used for the second UE to receive a signal from
the first UE.
[0009] In another aspect of the present invention, provided herein
is a method for an eNB to support signal transmission from a first
UE to a second UE, the method including: receiving from the first
UE a resource allocation request for signal transmission from the
first UE to the second UE; and transmitting to the first UE and the
second UE scheduling information for signal transmission from the
first UE to the second UE. The scheduling information may include
information on an uplink resource used for the first UE to transmit
a signal to the second UE.
[0010] In another aspect of the present invention, provided herein
is a transceiver for transmitting a signal to another device,
including: a transmission module for transmitting signals to an eNB
and the other device; a reception module for receiving a signal
from the eNB; and a processor for controlling the transceiver
including the transmission module and the reception module. The
processor may be configured to request the eNB to allocate a
resource for signal transmission to the other device, to receive
scheduling information for signal transmission to the other device
from the eNB and to transmit a signal to the other device on the
basis of the scheduling information. The scheduling information may
include information on an uplink resource used for the transceiver
to transmit a signal to the other device.
[0011] In another aspect of the present invention, provided herein
is a transceiver for receiving a signal from another device,
including: a transmission module for transmitting a signal to an
eNB; a reception module for receiving signals from the eNB and the
other device; and a processor for controlling the transceiver
including the transmission module and the reception module. The
processor may be configured to receive from the eNB scheduling
information for signal transmission from the other device to the
transceiver and to receive a signal from the other device on the
basis of the scheduling information. The scheduling information may
include information on an uplink resource used for the transceiver
to receive a signal from the other device.
[0012] In another aspect of the present invention, provided herein
is an eNB device supporting signal transmission from a first
transceiver to a second transceiver, including: a transmission
module for transmitting signals to the first and second
transceivers; a reception module for receiving signals from the
first and second transceivers; and a processor for controlling the
eNB device including the transmission module and the reception
module. The processor may be configured to receive, from the first
transceiver, a resource allocation request for signal transmission
from the first transceiver to the second transceiver and to
transmit to the first and second transceivers scheduling
information for signal transmission from the first transceiver to
the second transceiver. The scheduling information may include
information on an uplink resource used for the first transceiver to
transmit a signal to the second transceiver.
[0013] The following may be commonly applied to the above-described
embodiments of the present invention.
[0014] The first UE may transmit a signal for channel state
measurement in the second UE.
[0015] One or more of a physical uplink control channel (PUCCH), a
physical uplink shared channel (PUSCH), an uplink modulation
reference signal (UL DMRS), a sounding reference signal (SRS) and a
physical random access channel (PRACH) preamble may be transmitted
on the uplink resource from the first UE to the second UE.
[0016] One or more of a physical downlink control channel (PDCCH),
a physical downlink shared channel (PDSCH), a cell-specific
reference signal and a channel state information-reference signal
(CSI-RS) may be transmitted on the uplink resource from the first
UE to the second UE.
[0017] A scheduling request or a PRACH preamble may be transmitted
from the first UE to the eNB, and the first UE may receive an
uplink grant from the eNB and transmit additional information
including one or more of the ID of the first UE, the ID of the
second UE and a buffer state report of the first UE to the eNB
using the uplink grant.
[0018] ACK/NACK information for the signal received from the first
UE may be transmitted from the second UE to the eNB.
[0019] The ACK/NACK information for the signal received from the
first UE may be transmitted to the eNB along with ACK/NACK
information for a signal received from the eNB.
[0020] ACK/NACK information for a maximum of N signals received by
the second UE may be transmitted on a single uplink subframe, and N
may be a fixed value in both a case in which the ACK/NACK
information for the signal received from the first UE is
transmitted in the single uplink subframe and a case in which the
ACK/NACK information for the signal received from the first UE is
not transmitted in the single uplink subframe.
[0021] When the signal from the first UE is received in a subframe
n, the ACK/NACK information for the signal received from the first
UE may transmitted in a subframe in which ACK/NACK information for
downlink data from the eNB is transmitted when the downlink data is
received from the eNB in the subframe n, an initial uplink subframe
from among subframes after a predetermined process time from the
subframe n, or an initial subframe scheduled to transmit uplink
data from among subframes after a predetermined process time from
the subframe n.
[0022] The second UE may receive, from the first UE, a signal for
measuring the state of a channel from the first UE and transmit
channel state information to the eNB.
[0023] When the channel state information is transmitted in a
subframe n, a channel state information reference resource may be
set to a latest uplink subframe belonging to the same uplink HARQ
process as that to which the subframe n belongs from among
subframes prior to the subframe n, a latest uplink subframe from
among subframes a predetermined process time in advance of the
subframe n, a latest uplink subframe from among subframes a
predetermined process time in advance of the subframe n and after a
subframe in which control information for requesting transmission
of the channel state information is received, or a latest subframe
scheduled to transmit the signal for measuring the state of the
channel from the first UE from among subframes a predetermined
process time in advance of the subframe n.
[0024] When uplink transmission of the second UE is set in the
uplink resource, uplink transmission of the second UE may be
dropped.
[0025] Above description and the following detailed description of
the present invention are exemplary and are for the purpose of
additional explanation of the claims.
Advantageous Effects
[0026] According to the present invention, it is possible to
provide a method of performing D2D communication efficiently and
correctly.
[0027] The effects of the present invention are not limited to the
above-described effects and other effects which are not described
herein will become apparent to those skilled in the art from the
following description.
DESCRIPTION OF DRAWINGS
[0028] The accompanying drawings, which are included to provide a
further understanding of the invention, illustrate embodiments of
the invention and together with the description serve to explain
the principle of the invention. In the drawings:
[0029] FIG. 1 illustrates a downlink radio frame structure;
[0030] FIG. 2 illustrates a resource grid of a downlink slot;
[0031] FIG. 3 illustrates a downlink subframe structure;
[0032] FIG. 4 illustrates an uplink subframe structure;
[0033] FIG. 5 illustrates a configuration of a wireless
communication system having multiple antennas;
[0034] FIG. 6 illustrates mapping of PUCCH formats to PUCCH regions
in uplink physical resource blocks;
[0035] FIG. 7 illustrates an ACK/NACK channel structure in a normal
CP case;
[0036] FIG. 8 illustrates a CQI channel structure in the normal CP
case;
[0037] FIG. 9 illustrates an ACK/NACK channel structure using block
spreading;
[0038] FIG. 10 illustrates carrier aggregation;
[0039] FIG. 11 illustrates cross-carrier scheduling;
[0040] FIG. 12 illustrates the concept of D2D communication;
[0041] FIG. 13 is a flowchart illustrating an exemplary D2D
communication method according to the present invention;
[0042] FIG. 14 illustrates ACK/NACK information transmission for
D2D transmission;
[0043] FIG. 15 illustrates CSI reference resource configuration;
and
[0044] FIG. 16 illustrates configurations of a transmitter and a
receiver according to the present invention.
BEST MODE
[0045] The following embodiments are proposed by combining
constituent components and characteristics of the present invention
according to a predetermined format. The individual constituent
components or characteristics should be considered to optional
factors on the condition that there is no additional remark. If
required, the individual constituent components or characteristics
may not be combined with other components or characteristics. Also,
some constituent components and/or characteristics may be combined
to implement the embodiments of the present invention. The order of
operations to be disclosed in the embodiments of the present
invention may be changed. Some components or characteristics of any
embodiment may also be included in other embodiments, or may be
replaced with those of the other embodiments as necessary.
[0046] The embodiments of the present invention are disclosed on
the basis of a data communication relationship between a base
station and a terminal. In this case, the base station is used as a
terminal node of a network via which the base station can directly
communicate with the terminal. Specific operations to be conducted
by the base station in the present invention may also be conducted
by an upper node of the base station as necessary.
[0047] In other words, it will be obvious to those skilled in the
art that various operations for enabling the base station to
communicate with the terminal in a network composed of several
network nodes including the base station will be conducted by the
base station or other network nodes other than the base station.
The term "Base Station (BS)" may be replaced with a fixed station,
Node-B, eNode-B (eNB), or an access point as necessary. The term
"relay" may be replaced with a Relay Node (RN) or a Relay Station
(RS). The term "terminal" may also be replaced with a User
Equipment (UE), a Mobile Station (MS), a Mobile Subscriber Station
(MSS) or a Subscriber Station (SS) as necessary.
[0048] It should be noted that specific terms disclosed in the
present invention are proposed for convenience of description and
better understanding of the present invention, and the use of these
specific terms may be changed to other formats within the technical
scope or spirit of the present invention.
[0049] In some instances, well-known structures and devices are
omitted in order to avoid obscuring the concepts of the present
invention and the important functions of the structures and devices
are shown in block diagram form. The same reference numbers will be
used throughout the drawings to refer to the same or like
parts.
[0050] Exemplary embodiments of the present invention are supported
by standard documents disclosed for at least one of wireless access
systems including an Institute of Electrical and Electronics
Engineers (IEEE) 802 system, a 3.sup.rd Generation Project
Partnership (3GPP) system, a 3GPP Long Term Evolution (LTE) system,
an LTE-Advance (LTE-A) system, and a 3GPP2 system. In particular,
the steps or parts, which are not described to clearly reveal the
technical idea of the present invention, in the embodiments of the
present invention may be supported by the above documents. All
terminology used herein may be supported by at least one of the
above-mentioned documents.
[0051] The following embodiments of the present invention can be
applied to a variety of wireless access technologies, for example,
CDMA (Code Division Multiple Access), FDMA (Frequency Division
Multiple Access), TDMA (Time Division Multiple Access), OFDMA
(Orthogonal Frequency Division Multiple Access), SC-FDMA (Single
Carrier Frequency Division Multiple Access), and the like. CDMA may
be embodied through wireless (or radio) technology such as UTRA
(Universal Terrestrial Radio Access) or CDMA2000. TDMA may be
embodied through wireless (or radio) technology such as GSM (Global
System for Mobile communications)/GPRS (General Packet Radio
Service)/EDGE (Enhanced Data Rates for GSM Evolution). OFDMA may be
embodied through wireless (or radio) technology such as Institute
of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE
802.16 (WiMAX), IEEE 802-20, and E-UTRA (Evolved UTRA). UTRA is a
part of UMTS (Universal Mobile Telecommunications System). 3GPP
(3rd Generation Partnership Project) LTE (long term evolution) is a
part of E-UMTS (Evolved UMTS), which uses E-UTRA. 3GPP LTE employs
OFDMA in downlink and employs SC-FDMA in uplink. LTE--Advanced
(LTE-A) is an evolved version of 3GPP LTE. WiMAX can be explained
by an IEEE 802.16e (WirelessMAN-OFDMA Reference System) and an
advanced IEEE 802.16m (WirelessMAN-OFDMA Advanced System). For
clarity, the following description focuses on 3GPP LTE and 3GPP
LTE-A systems. However, technical features of the present invention
are not limited thereto.
[0052] A downlink radio frame structure will now be described with
reference to FIG. 1.
[0053] In a cellular OFDM wireless packet communication system, an
uplink/downlink data packet is transmitted on a subframe basis and
one subframe is defined as a predetermined time interval including
a plurality of OFDM symbols. 3GPP LTE standard supports a type-1
radio frame structure applicable to frequency division duplex (FDD)
and a type-2 radio frame structure applicable to time division
duplex (TDD).
[0054] FIG. 1(a) illustrates the type-1 radio frame structure. A
downlink radio frame is divided into 10 subframes. Each subframe is
further divided into two slots in the time domain. A unit time
during which one subframe is transmitted is defined as transmission
time interval (TTI). For example, one subframe may be lms in
duration and one slot may be 0.5 ms in duration. A slot may include
a plurality of orthogonal frequency division multiplexing (OFDM)
symbols in the time domain and includes a plurality of resource
blocks (RBs) in the frequency domain. Because the 3GPP LTE system
adopts OFDMA for downlink, an OFDM symbol represents one symbol
period. An OFDM symbol may be referred to as an SC-FDMA symbol or
symbol period. A Resource Block (RB) is a resource allocation unit
including a plurality of contiguous subcarriers in a slot.
[0055] The number of OFDM symbols included in one slot depends on
cyclic prefix (CP) configuration. CP is divided into an extended CP
and a normal CP. For example, when OFDM symbols are configured
according to normal CP, the number of OFDM symbols included in one
slot may be 7. When the OFDM symbols are configured according to
extended CP, the duration of one OFDM symbol increases and thus the
number of OFDM symbols included in one slot is smaller than the
number of OFDM symbols included in one slot when the OFDM symbols
are configured using the normal CP. In the extended CP case, the
number of OFDM symbols included in one slot may be 6, for example.
When a channel status is unstable, for example, when a UE moves at
a high speed, the extended CP can be used to reduce inter-symbol
interference.
[0056] When the normal CP is used, one slot includes 7 OFDM
symbols, and thus one subframe includes 14 OFDM symbols. In this
case, up to three OFDM symbols at the start of each subframe can be
allocated to a physical downlink control channel (PDCCH) and the
other three OFDM symbols can be allocated to a physical downlink
shared channel (PDSCH).
[0057] FIG. 1(b) illustrates the type-2 radio frame structure. The
type-2 radio frame includes two half frames each having 5
subframes, a downlink pilot time slot (DwPTS), a guard period (GP),
and an uplink pilot time slot (UpPTS). Each subframe includes two
slots. The DwPTS is used for initial cell search, synchronization,
or channel estimation in a UE, whereas the UpPTS is used for
channel estimation in an eNB and uplink transmission
synchronization in a UE. The GP is a period between a downlink and
an uplink, for eliminating interference with the uplink caused by
multi-path delay of a downlink signal. A subframe is composed of
two slots irrespective of radio frame type.
[0058] The aforementioned radio frame structure is purely exemplary
and thus the number of subframes included in a radio frame, the
number of slots included in a subframe, or the number of symbols
included in a slot may vary.
[0059] FIG. 2 illustrates a resource grid for a downlink slot. A
downlink slot includes 7 OFDM symbols in the time domain and an RB
includes 12 subcarriers in the frequency domain, which does not
limit the scope and spirit of the present invention. For example, a
slot includes 7 OFDM symbols in the case of normal CP, whereas a
slot includes 6 OFDM symbols in the case of extended CP. Each
element of the resource grid is referred to as a resource element
(RE). An RB includes 12.times.7 REs. The number of RBs in a
downlink slot, N.sup.DL depends on a downlink transmission
bandwidth. An uplink slot may have the same structure as a downlink
slot.
[0060] FIG. 3 illustrates a downlink subframe structure. Up to
three OFDM symbols at the start of the first slot in a downlink
subframe are used for a control region to which control channels
are allocated and the other OFDM symbols of the downlink subframe
are used for a data region to which a PDSCH is allocated. Downlink
control channels used in 3GPP LTE include a physical control format
indicator channel (PCFICH), a physical downlink control channel
(PDCCH), and a physical hybrid automatic repeat request (ARQ)
indicator channel (PHICH). The PCFICH is located in the first OFDM
symbol of a subframe, carrying information about the number of OFDM
symbols used for transmission of control channels in the subframe.
The PHICH delivers a HARQ acknowledgment/negative acknowledgment
(ACK/NACK) signal in response to an uplink transmission. Control
information carried on the PDCCH is called downlink control
information (DCI). The DCI includes uplink resource allocation
information, downlink resource allocation information or an uplink
transmit (Tx) power control command for an arbitrary UE group. The
PDCCH delivers information about resource allocation and a
transport format for a Downlink Shared Channel (DL-SCH), resource
allocation information about an Uplink Shared Channel (UL-SCH),
paging information of a Paging Channel (PCH), system information on
the DL-SCH, information about resource allocation for a
higher-layer control message such as a Random Access Response
transmitted on the PDSCH, a set of transmission power control
commands for individual UEs of a UE group, transmission power
control information, Voice Over Internet Protocol (VoIP) activation
information, etc. A plurality of PDCCHs may be transmitted in the
control region. A UE may monitor a plurality of PDCCHs. A PDCCH is
formed by aggregation of one or more consecutive Control Channel
Elements (CCEs). A CCE is a logical allocation unit used to provide
a PDCCH at a coding rate based on the state of a radio channel. A
CCE corresponds to a plurality of REs. The format of a PDCCH and
the number of available bits for the PDCCH are determined according
to the correlation between the number of CCEs and a coding rate
provided by the CCEs. An eNB determines the PDCCH format according
to DCI transmitted to a UE and adds a Cyclic Redundancy Check (CRC)
to control information. The CRC is masked by an Identifier (ID)
known as a Radio Network Temporary Identifier (RNTI) according to
the owner or usage of the PDCCH. If the PDCCH is directed to a
specific UE, its CRC may be masked by a cell-RNTI (C-RNTI) of the
UE. If the PDCCH carries a paging message, the CRC of the PDCCH may
be masked by a Paging Indicator Identifier (P-RNTI). If the PDCCH
carries system information, particularly, a System Information
Block (SIB), its CRC may be masked by a system information ID and a
System Information RNTI (SI-RNTI). To indicate that the PDCCH
carries a Random Access Response in response to a Random Access
Preamble transmitted by a UE, its CRC may be masked by a Random
Access-RNTI (RA-RNTI).
[0061] FIG. 4 illustrates an uplink subframe structure. An uplink
subframe may be divided into a control region and a data region in
the frequency domain. A physical uplink control channel (PUCCH)
carrying uplink control information is allocated to the control
region and a physical uplink shared channel (PUSCH) carrying user
data is allocated to the data region. To maintain single carrier
property, a UE does not transmit a PUSCH and a PUCCH
simultaneously. A PUCCH for a UE is allocated to an RB pair in a
subframe. The RBs of the RB pair occupy different subcarriers in
two slots. Thus it is said that the RB pair allocated to the PUCCH
is frequency-hopped over a slot boundary.
[0062] MIMO System Modeling
[0063] FIG. 5 illustrates the configuration of a communication
system including multiple antennas.
[0064] Referring to FIG. 5(a), when both the number of Tx antennas
and the number of Rx antennas respectively to N.sub.T and N.sub.R,
a theoretical channel transmission capacity is increased, compared
to use of a plurality of antennas at only one of a transmitter and
a receiver. The channel transmission capacity is increased in
proportion to the number of antennas. Therefore, transmission rate
and frequency efficiency can be increased remarkably. Given a
maximum transmission rate R.sub.o that may be achieved with a
single antenna, the transmission rate may be increased, in theory,
to the product of R.sub.o and a transmission rate increase rate
R.sub.i illustrated in Equation 1 due to an increase in channel
transmission capacity in case of multiple antennas.
R.sub.i=min(N.sub.T, N.sub.R) [Equation 1]
[0065] For instance, a MIMO communication system with 4 Tx antennas
and 4 Rx antennas may achieve a four-fold increase in transmission
rate theoretically, relative to a single-antenna system. The
theoretical increase in transmission rate of MIMO communication was
demonstrated in the mid-1990s, various technologies for improving
data rate have been actively studied since then and are now
employed in various wireless communication standards such as
3.sup.rd generation mobile communication and next-generation
wireless LAN.
[0066] A variety of research such as information theory research
related to calculation of multi-antenna throughput in various
channel environments and multiple access environments, research on
radio channel measurement and model derivation in MIMO systems and
research on time spatial signal processing technology for
improvement of transmission reliability and data rate are
underway.
[0067] Communication in a MIMO system will be described in detail
through mathematical modeling. It is assumed that N.sub.T Tx
antennas and N.sub.R Rx antennas are present.
[0068] Regarding a transmission signal, up to N.sub.T pieces of
information can be transmitted through the N.sub.T Tx antennas, as
expressed as the following vector.
S=[S.sub.1, S.sub.2, . . . , S.sub.N.sub.T] [Equation 2]
[0069] A different transmission power may be applied to each piece
of transmission information, S.sub.1, S.sub.2, . . . ,
S.sub.N.sub.T. Let the transmission power levels of the
transmission information be denoted by P.sub.1, P.sub.2, . . . ,
P.sub.N.sub.T, respectively. Then the transmission power-controlled
transmission information vector is given as follows.
S=[S.sub.1, S.sub.2, . . . , S.sub.N.sub.T].sup.T=[P.sub.S.sub.1,
P.sub.S.sub.2, . . . , P.sub.S.sub.NT].sup.T [Equation 3]
[0070] The transmission power-controlled transmission information
vector S may be expressed as follows, using a diagonal matrix P of
transmission power.
s ^ = [ P 1 0 P 2 0 P N T ] [ s 1 s 2 s N T ] = Ps [ Equation 4 ]
##EQU00001##
[0071] N.sub.T transmission signals x.sub.1, x.sub.2, . . . ,
x.sub.N.sub.T may be generated by multiplying the transmission
power-controlled information vectors by a weight matrix W. The
weight matrix W functions to appropriately distribute the
transmission information to the Tx antennas according to
transmission channel states, etc. These N.sub.T transmission
signals x.sub.1, x.sub.2, . . . , x.sub.N.sub.T are represented as
a vector X, which may be determined by Equation 5.
x = [ x 1 x 2 x i x N T ] = [ w 11 w 12 w 1 N T w 12 w 12 w 2 N T w
i 2 w i 2 w iN T w N T 1 w N T 2 w N T N T ] [ s ^ 1 s ^ 2 s ^ j s
^ N T ] = W s ^ = WPs [ Equation 5 ] ##EQU00002##
[0072] Herein, w.sub.ij denotes a weight between an i.sup.th Tx
antenna and a j.sup.th piece of information. W is called a weight
matrix or a precoding matrix.
[0073] Given N.sub.R Rx antennas, signals received at the
respective Rx antennas, y.sub.1, y.sub.2, . . . , y.sub.N.sub.R may
be represented as the following vector.
y=[y.sub.1, y.sub.2, . . . y.sub.N.sub.R].sup.T [Equation 6]
[0074] When channels are modeled in the MIMO communication system,
they may be distinguished according to the indexes of Tx and Rx
antennas and the channel between a j.sup.th Tx antenna and an
i.sup.th Rx antenna may be represented as h.sub.ij. It is to be
noted herein that the index of the Rx antenna precedes that of the
Tx antenna in h.sub.ij.
[0075] FIG. 5(b) illustrates channels from N.sub.T Tx antennas to
an i.sup.th Rx antenna. The channels may be represented as vectors
and matrices by grouping them. As illustrated in FIG. 5(b), the
channels from the N.sub.T Tx antennas to an i.sup.th Rx antenna may
be expressed as follows.
h.sub.i.sup.T=[h.sub.i1, h.sub.i2, . . . , h.sub.i.sub.NT]
[Equation 7]
[0076] Also, all channels from the N.sub.T Tx antennas to the
N.sub.R Rx antennas may be expressed as the following matrix.
H = [ h 1 T h 2 T h i T h N R T ] = [ h 11 h 12 h 1 N T h 12 h 12 h
2 N T h i 2 h i 2 h iN T h N R 1 h N R 2 h N R N T ] [ Equation 8 ]
##EQU00003##
[0077] Actual channels experience the above channel matrix H and
then are added with Additive White Gaussian Noise (AWGN). The AWGN
n.sub.1, n.sub.2, . . . , n.sub.N.sub.n added to the N.sub.R Rx
antennas is given as the following vector.
n=[n.sub.1, n.sub.2, . . . , n.sub.N.sub.R].sup.T [Equation 9]
[0078] From the above modeled equations, the received signal can be
expressed as follows.
y = [ y 1 y 2 y i y N R ] = [ h 11 h 12 h 1 N T h 12 h 12 h 2 N T h
i 2 h i 2 h iN T h N R 1 h N R 2 h N R N T ] [ x 1 x 2 x j x N T ]
+ [ n 1 n 2 n i n N R ] = Hx + n [ Equation 10 ] ##EQU00004##
[0079] In the meantime, the numbers of rows and columns in the
channel matrix H representing channel states are determined
according to the numbers of Tx and Rx antennas. The number of rows
is identical to that of Rx antennas, N.sub.R and the number of
columns is identical to that of Tx antennas, N.sub.T. Thus, the
channel matrix H is of size N.sub.RxN.sub.T.
[0080] In general, the rank of a matrix is defined as the smaller
between the numbers of independent rows and columns. Accordingly,
the rank of the matrix is not larger than the number of rows or
columns. The rank of the matrix H, rank(H) is limited as
follows.
rank(H).ltoreq.min(N.sub.T, N.sub.R) [Equation 11]
[0081] The rank of a matrix may be defined as the number of
non-zero Eigen values when the matrix is Eigen-value-decomposed.
Similarly, the rank of a matrix may be defined as the number of
non-zero singular values when the matrix is
singular-value-decomposed. Accordingly, the physical meaning of the
rank of a channel matrix can be a maximum number of channels
through which different pieces of information can be
transmitted.
[0082] In the specification, `rank` with respect to MIMO
transmission represents the number of paths through which signals
can be independently transmitted in a specific frequency resource
at a specific instance and `number of layers` refers to the number
of signal streams transmitted through each path. Since a
transmitter transmits as many layers as the number of ranks used
for signal transmission, the rank corresponds to the number of
layers unless otherwise mentioned.
[0083] Coordinated Multi-Point: CoMP
[0084] CoMP transmission/reception scheme (which is also referred
to as co-MIMO, collaborative MIMO or network MIMO) is proposed to
meet enhanced system performance requirements of 3GPP LTE-A. CoMP
can improve the performance of a UE located at a cell edge and
increase average sector throughput.
[0085] In a multi-cell environment having a frequency reuse factor
of 1, the performance of a UE located at a cell edge and average
sector throughput may decrease due to inter-cell interference
(ICI). To reduce ICI, a conventional LTE system uses a method for
allowing a UE located at a cell edge in an interfered environment
to have appropriate throughput using a simple passive scheme such
as fractional frequency reuse (FFR) through UE-specific power
control. However, it may be more preferable to reduce ICI or reuse
ICI as a signal that a UE desires rather than decreasing frequency
resource use per cell. To achieve this, CoMP can be applied.
[0086] CoMP applicable to downlink can be classified into joint
processing (JP) and coordinated scheduling/beamforming (CS/CB).
[0087] According to the JP, each point (eNB) of a CoMP coordination
unit can use data. The CoMP coordination unit refers to a set of
eNBs used for a coordinated transmission scheme. The JP can be
divided into joint transmission and dynamic cell selection.
[0088] The joint transmission refers to a scheme through which
PDSCHs are simultaneously transmitted from a plurality of points
(some or all CoMP coordination units). That is, data can be
transmitted to a single UE from a plurality of transmission points.
According to joint transmission, quality of a received signal can
be improved coherently or non-coherently and interference on other
UEs can be actively erased.
[0089] Dynamic cell selection refers to a scheme by which a PDSCH
is transmitted from one point (in a CoMP coordination unit). That
is, data is transmitted to a single UE from a single point at a
specific time, other points in the coordination unit do not
transmit data to the UE at the time, and the point that transmits
the data to the UE can be dynamically selected.
[0090] According to the CS/CB scheme, CoMP coordination units can
collaboratively perform beamforming of data transmission to a
single UE. Here, user scheduling/beaming can be determined
according to coordination of cells in a corresponding CoMP
coordination unit although data is transmitted only from a serving
cell.
[0091] In case of uplink, coordinated multi-point reception refers
to reception of a signal transmitted according to coordination of a
plurality of points geographically spaced apart from one another. A
CoMP reception scheme applicable to uplink can be classified into
joint reception (JR) and coordinated scheduling/beamforming
(CS/CB).
[0092] JR is a scheme by which a plurality of reception points
receives a signal transmitted over a PUSCH and CS/CB is a scheme by
which user scheduling/beamforming is determined according to
coordination of cells in a corresponding CoMP coordination unit
while one point receives a PUSCH.
[0093] A UE can receive data from multi-cell base stations
collaboratively using the CoMP system. The base stations can
simultaneously support one or more UEs using the same radio
frequency resource, improving system performance. Furthermore, a
base station may perform space division multiple access (SDMA) on
the basis of CSI between the base station and a UE.
[0094] In the CoMP system, a serving eNB and one or more
collaborative eNBs are connected to a scheduler through a backbone
network. The scheduler can operate by receiving channel information
about a channel state between each UE and each collaborative eNB,
measured by each eNB, through the backbone network. For example,
the scheduler can schedule information for collaborative MIMO
operation for the serving eNB and one or more collaborative eNBs.
That is, the scheduler can directly direct collaborative MIMO
operation to each eNB.
[0095] As described above, the CoMP system can be regarded as a
virtual MIMO system using a group of a plurality of cells.
Basically, a communication scheme of MIMO using multiple antennas
can be applied to CoMP.
[0096] Downlink Channel Status (CSI) Feedback
[0097] MIMO can be categorized into an open-loop scheme and a
closed-loop scheme. The open-loop scheme performs MIMO transmission
at a transmitter without feedback of CSI from a MIMO receiver,
whereas the closed-loop scheme performs MIMO transmission at the
transmitter using feedback of CSI from the MIMO receiver. In
closed-loop MIMO, each of the transmitter and the receiver can
perform beamforming based on CSI to obtain MIMO Tx antenna
multiplexing gain. The transmitter (e.g. eNB) can allocate an
uplink control channel or an uplink shared channel to the receiver
(e.g. UE) such that the receiver can feed back CSI.
[0098] CSI fed back may include a rank indicator (RI), a precoding
matrix index (PMI) and a channel quality indictor (CQI).
[0099] The RI indicates information about a channel rank. The
channel rank represents a maximum number of layers (or streams)
through which different pieces of information can be transmitted
through the same time-frequency resource. The RI is determined by
long term fading of a channel, and thus the RI can be fed back to
an eNB at a longer period than the PMI and CQI.
[0100] The PMI is information about a precoding matrix used for
transmission from a transmitter and is a value in which spatial
characteristics of a channel are reflected. Precoding refers to
mapping a transport layer to a transmit antenna. A layer-to-antenna
mapping relation can be determined by a precoding matrix. The PMI
indicates a precoding matrix index of an eNB preferred by a UE
based on a metric such as signal-interference plus noise ratio
(SINR). To reduce feedback overhead of precoding information, the
transmitter and receiver can share a codebook including precoding
matrices and only an index indicating a specific precoding matrix
in the codebook can be fed back.
[0101] The CQI indicates channel quality or channel intensity. The
CQI can be represented as a predetermined MCS combination. That is,
a fed back CQI index indicates a corresponding modulation scheme
and a code rate. The CQI represents a value in which a reception
SINR that can be obtained when an eNB configures a spatial channel
using the PMI is reflected.
[0102] In a system supporting an extended antenna configuration
(e.g. LTE-A), additional multi-user diversity is obtained using
multi-user MIMO (MU-MIMO). When an eNB performs downlink
transmission using CSI fed back by one of multiple UEs, it is
necessary to prevent downlink transmission from interfering with
other UEs since an interference channel is present between UEs
multiplexed in the antenna domain in MU-MIMO. Accordingly, MU-MIMO
requires more accurate CSI feedback than single user MIMO
(SU-MIMO).
[0103] A new CSI feedback scheme that improves CSI composed of the
RI, PMI and CQI can be applied in order to measure and report more
accurate CSI. For example, precoding information fed back by a
receiver can be indicated by a combination of two PMIs. One (first
PMI) of the two PMIs is long term and/or wideband information and
may be denoted as W1. The other PMI (second PMI) is short term
and/or subband information and may be denoted as W1. A final PMI
can be determined by a combination (or function) of W1 and W2. For
example, if the final PMI is W, W can be defined as W=W1*W2 or
W=W2*W1.
[0104] Here, W1 reflects frequency and/or temporal average
characteristics of a channel. In other words, W1 can be defined as
CSI reflecting characteristics of a long-term channel in the time
domain, characteristics of a wideband channel in the frequency
domain or characteristics of a long-term and wideband channel. To
simply represent these characteristics of W1, W1 is referred to as
long term-wideband CSI (or long term-wideband PMI) in this
specification.
[0105] W2 reflects instantaneous channel characteristics compared
to W1. In other words, W2 can be defined as CSI reflecting
characteristics of a short-term channel in the time domain,
characteristics of a subband channel in the frequency domain or
characteristics of a short-term and subband channel. To simply
represent these characteristics of W2, W2 is referred to as short
term-subband CSI (or short term-subband PMI) in this
specification.
[0106] To determine a final precoding matrix W from two different
pieces of information (e.g. W1 and W2) representing channel states,
it is necessary to configure separate codebooks (i.e. a first
codebook for W1 and a second codebook for W2) composed of precoding
matrices representing the information. A codebook configured in
this manner may be called a hierarchical codebook. Determination of
a final codebook using the hierarchical codebook is called
hierarchical codebook transformation.
[0107] A codebook can be transformed using a long-term covariance
matrix of a channel, represented by Equation 12, as exemplary
hierarchical codebook transformation.
W=norm(W1W2) [Equation 12]
[0108] In Equation 12, W1 (long term-wideband PMI) denotes an
element (i.e. codeword) constituting a codebook (e.g. first
codebook) generated to reflect long term-wideband channel
information. That is, W1 corresponds to a precoding matrix included
in the first codebook that reflects the long term-wideband channel
information. W2 (short term-subband PMI) represents a codeword
constituting a codebook (e.g. second codebook) generated to reflect
short term/subband channel information. That is, W2 corresponds to
a precoding matrix included in the second codebook that reflects
the short term-subband channel information. W is a codeword of a
transformed final codebook and norm(A) denotes a matrix in which
the norm of each column of matrix A is normalized to 1.
[0109] W1 and W2 may have structures as represented by Equation
13.
W 1 ( i ) = [ X i 0 0 X i ] W 2 ( j ) = [ e M k e M l e M m .alpha.
j e M k .beta. j e M l .gamma. j e M m ] r columns ( if rank = r )
[ Equation 13 ] ##EQU00005##
[0110] In Equation 13, W1 can be defined as a block diagonal matrix
and blocks correspond to the same matrix X.sub.i. A block X.sub.i
can be defined as a (Nt/2).times.M matrix. Here, Nt denotes the
number of Tx antennas. e.sub.M.sup.p(p=k, l, . . . , m) is an
M.times.1 vector wherein a p-th element of M vector elements
represents 1 and other elements represent 0. When W1 is multiplied
by e.sub.M.sup.p, a p-th column is selected from columns of W1 and
thus this vector can be called a selection vector. The number of
vectors fed back at a time to represent a long term-wideband
channel increases as M increases, to thereby improve feedback
accuracy. However, the codebook size of W1 fed back with low
frequency decreases and the codebook size of W2 fed back with high
frequency increases as M increases, increasing feedback overhead.
That is, there is a tradeoff between feedback overhead and feedback
accuracy. Accordingly, M can be determined such that feedback
overhead is not excessively increased and appropriate feedback
accuracy is maintained. As to W2, .alpha..sub.j, .beta..sub.j and
.gamma..sub.j are predetermined phase values. In Equation 13,
1.ltoreq.k,l,m.ltoreq.M and k, l and m are integers.
[0111] The codebook structure represented by Equation 13 uses a
cross polarized antenna configuration and reflects correlation
characteristics of a channel, generated when antenna spacing is
narrow (when a distance between neighboring antennas is less than
half a signal wavelength). For example, cross polarized antenna
configurations may be represented as shown in Table 1.
TABLE-US-00001 TABLE 1 2Tx cross-polarized antenna configuration
##STR00001## 4Tx cross-polarized antenna configuration ##STR00002##
8Tx cross-polarized antenna configuration ##STR00003##
[0112] In Table 1, an 8Tx cross polarized antenna configuration is
composed of two antenna groups having orthogonal polarizations.
Antennas belonging to antenna group 1 (antennas 1, 2, 3 and 4) may
have the same polarization (e.g. vertical polarization) and
antennas belonging to antenna group 2 (antennas 5, 6 7 and 8) may
have the same polarization (e.g. horizontal polarization). The two
antenna groups are co-located. For example, antennas 1 and 5 can be
co-located, antennas 2 and 6 can be co-located, antennas 3 and 7
can be co-located and antenna 2 and 8 can be co-located. In other
words, antennas in an antenna group have the same polarization as
in a uniform linear array (ULA) and a correlation between antennas
in an antenna group has a linear phase increment characteristic.
Furthermore, a correlation between antenna groups has a phase
rotation characteristic.
[0113] Since a codebook is composed of values obtained by
quantizing a channel, it is necessary to design the codebook by
reflecting actual channel characteristics therein. To describe
reflection of actual channel characteristics in codewords of a
codebook designed as represented by Equation 13, a rank-1 codebook
is exemplified. Equation 14 represents determination of a final
codeword W by multiplying codeword W1 by codeword W2 in the case of
rank 1.
W 1 ( i ) * W 2 ( j ) = [ X i ( k ) .alpha. j X i ( k ) ] [
Equation 14 ] ##EQU00006##
[0114] In Equation 14, the final codeword is represented by a
vector of Nt.times.1 and is composed of an upper vector X.sub.i(k)
and a lower vector .alpha..sub.jX.sub.i(k) which respectively
represent correlations between horizontal antenna groups and
vertical antenna groups of cross polarized antennas. X.sub.i(k) is
preferably represented as a vector (e.g. DFT matrix) having linear
phase increment in which correlation between antennas in each
antenna group is reflected.
[0115] When the above-described codebook is used, higher channel
feedback accuracy can be achieved compared to a case in which a
single codebook is used. Single-cell MU-MIMO can be performed using
high accuracy channel feedback and thus high accuracy channel
feedback is necessary for CoMP operation. For example, plural eNBs
cooperatively transmit the same data to a specific UE in CoMP JT
operation, and thus this system can be theoretically regarded as a
MIMO system in which plural antennas are geographically
distributed. That is, even when MU-MIMO operation is performed in
CoMP JT, high channel information accuracy is necessary to avoid
interference between co-scheduled UEs. In addition, CoMP CB also
requires accurate channel information in order to avoid
interference of a neighboring cell, applied to a serving cell.
[0116] Reference Signal (RS)
[0117] Since a packet is transmitted through a radio channel in a
wireless communication system, a signal may be distorted during
transmission. A receiver needs to correct the distorted signal
using channel information in order to correctly receive the
distorted signal. To detect channel information, a signal known to
both the receiver and a transmitter is transmitted and channel
information is detected using a degree of distortion of the signal
when the signal is received through a certain channel. This signal
is called a pilot signal or a reference signal. When multiple
antennas are used to transmit and receive data, a correct signal
can be received only when channel state between each Tx antenna and
each Rx antenna is detected. Accordingly, a reference signal is
required for each Tx antenna.
[0118] In legacy wireless communication systems (e.g. 3GPP LTE
release-8 or release-9), a downlink reference signal defines a
common reference signal (CRS) shared by all UEs in a cell and a
dedicated reference signal (DRS) dedicated to a specific UE.
Information for channel estimation and demodulation can be provided
according to these reference signals.
[0119] A receiver (UE) can estimate channel state from the CRS and
feed back an indicator related to channel quality, such as a
channel quality indicator (CQI), a precoding matrix index (PMI)
and/or a rank indicator (RI), to a transmitter (eNB). The CRS may
be called a cell-specific reference signal.
[0120] The DRS can be transmitted through a corresponding RE when
data demodulation is needed. Presence or absence of the DRS may be
signaled to the UE by a higher layer. In addition, the fact that
the DRS is valid only when a corresponding PDSCH is mapped may be
signaled to the UE. The DRS may be called a UE-specific reference
signal or a demodulation reference signal.
[0121] To provide higher spectral efficiency than 3GPP LTE (e.g.
LTE release-8 or release-9), a system (e.g. LTE-A (Advanced))
having an extended antenna configuration may be designed. The
extended antenna configuration may be an 8Tx antenna configuration.
The system having the extended antenna configuration needs to
support UEs operating in a conventional antenna configuration. That
is, the system needs to support backward compatibility.
Accordingly, it is necessary to support a reference signal pattern
according to the conventional antenna configuration and to design a
new reference signal pattern for an additional antenna
configuration.
[0122] Since LTE defines the downlink reference signal only for a
maximum of 4 antenna ports, if an eNB has up to 8 downlink Tx
antennas in LTE-A, RSs for up to 8 Tx antennas need to be
additionally defined. Both an RS for channel measurement and an RS
for data demodulation need to be considered as the RSs for up to 8
Tx antennas.
[0123] When the RSs for up to 8 Tx antennas are added to a
time-frequency region in which a CRS defined in LTE is transmitted
per subframe through a whole band, RS overhead excessively
increases during RS transmission. Therefore, it is necessary to
consider reduction of RS overhead when the RSs for up to 8 Tx
antennas are newly designed.
[0124] RSs newly introduced to LTE-A may be categorized into a
channel state information RS (CSI-RS) for channel measurement for
calculation/selection of a RI, PMI, CQI, etc. and a demodulation RS
(DM RS) for demodulation of data transmitted through a maximum of 8
Tx antennas.
[0125] The CSI-RS is designed mainly for channel measurement,
unlike the CRS of LTE, which is used for channel measurement,
handover measurement and data demodulation. The CSI-RS may also be
used for handover measurement. Since the CSI-RS is mainly used to
obtain channel state information, the CSI-RS need not be
transmitted per subframe unlike the CRS of LTE. Accordingly, the
CSI-RS can be designed such that it is intermittently (e.g.
periodically) transmitted in the time domain to reduce CSI-RS
overhead.
[0126] When data is transmitted on a downlink subframe, a DM RS is
transmitted to a UE scheduled to receive the data. A DM RS for a
specific UE can be designed such that it is transmitted only in a
resource region for which the specific UE is scheduled, that is, a
time-frequency region in which data for the specific UE is
transmitted.
[0127] Reference signals transmitted on uplink include a UL DMRS
and a sounding reference signal (SRS). The UL DMRS is a reference
signal transmitted for PUSCH demodulation and may be transmitted on
the fourth SC-FDMA symbol from among seven SC-FDMA symbols of each
slot in the normal CP case. The SRS is described in detail
below.
[0128] Sounding Reference Signal (SRS)
[0129] An SRS is used for an eNB to measure channel quality and
perform uplink frequency-selective scheduling based on the channel
quality measurement. The SRS is not associated with data and/or
control information transmission. However, the usages of the SRS
are not limited thereto. The SRS may also be used for enhanced
power control or for supporting various start-up functions of
non-scheduled UEs. The start-up functions may include, for example,
an initial modulation and coding scheme (MCS), initial power
control for data transmission, timing advance, and frequency
non-selective scheduling (in which a transmitter selectively
allocates a frequency resource to the first slot of a subframe and
then pseudo-randomly hops to another frequency resource in the
second slot of the subframe).
[0130] The SRS may be used for measuring downlink channel quality
on the assumption of the reciprocity of a radio channel between the
downlink and the uplink. This assumption is valid especially in a
time division duplex (TDD) system in which the downlink and the
uplink share the same frequency band and are distinguished by
time.
[0131] A subframe in which a UE within a cell is supposed to
transmit an SRS is indicated by cell-specific broadcast signaling.
A 4-bit cell-specific parameter `srsSubframeConfiguration`
indicates 15 possible configurations for subframes carrying SRSs in
each radio frame. These configurations may provide flexibility with
which SRS overhead can be adjusted according to network deployment
scenarios. The other one configuration (a 16.sup.th configuration)
represented by the parameter is perfect switch-off of SRS
transmission in a cell, suitable for a cell serving high-speed UEs,
for example.
[0132] An SRS is always transmitted in the last SC-FDMA symbol of a
configured subframe. Therefore, an SRS and a DMRS are positioned in
different SC-FDMA symbols. PUSCH data transmission is not allowed
in an SC-FDMA symbol designated for SRS transmission. Accordingly,
even the highest sounding overhead (in the case where SRS symbols
exist in all subframes) does not exceed 7%.
[0133] Each SRS symbol is generated for a given time unit and
frequency band, using a base sequence (a random sequence or
Zadoff-Chu (ZC)-based sequence set), and all UEs within a cell use
the same base sequence. SRS transmissions in the same time unit and
the same frequency band from a plurality of UEs within a cell are
distinguished orthogonally by different cyclic shifts of the base
sequence allocated to the plurality of UEs. Although the SRS
sequences of different cells may be distinguished by allocating
different base sequences to the cells, orthogonality is not ensured
between the different base sequences.
[0134] Physical Uplink Control Channel (PUCCH)
[0135] Uplink control information (UCI) transmitted on a PUCCH may
include a scheduling request (SR), HARQ ACK/NACK information, and
downlink channel measurement information.
[0136] The HARQ ACK/NACK information may be generated according to
whether a downlink data packet on a PDSCH is successfully decoded.
In conventional wireless communication systems, 1 bit is
transmitted as ACK/NACK information for downlink single codeword
transmission and 2 bits are transmitted as the ACK/NACK information
for downlink 2-codeword transmission.
[0137] The channel measurement information represents feedback
information about a multiple input multiple output (MIMO) scheme
and may include a channel quality indicator (CQI), a precoding
matrix index (PMI), and a rank indicator (RI) which may be
collectively referred to as a CQI. 20 bits per subframe may be used
to transmit the CQI.
[0138] A PUCCH can be modulated using binary phase shift keying
(BPSK) and quadrature phase shift keying (QPSK). Control
information of a plurality of UEs can be transmitted through a
PUCCH. When code division multiplexing (CDM) is performed in order
to distinguish signals of the UEs from one another, a length-12
constant amplitude zero autocorrelation (CAZAC) sequence is used.
The CAZAC sequence is suitable to increase coverage by reducing a
peak-to-average power ratio (PAPR) of a UE or cubic metric (CM)
because it maintain a specific amplitude in the time domain and the
frequency domain. ACK/NACK information with respect to downlink
data transmitted through a PUCCH is covered using an orthogonal
sequence or an orthogonal cover (OC).
[0139] Control information signals transmitted on a PUCCH may be
distinguished using cyclically shifted sequences having different
cyclic shift (CS) values. A cyclically shifted sequence may be
generated by cyclically shifting a base sequence by a specific CS
amount. The specific CS amount is indicated by a CS index. The
number of available CSs may vary according to channel delay spread.
Various types of sequences may be used as the base sequence and the
aforementioned CAZAC sequence is an example of the various
sequences.
[0140] The amount of control information that can be transmitted by
a UE through a subframe can be determined according to the number
of SC-FDMA symbols (i.e. SC-FDMA symbols other than SC-FDMA symbols
used for reference signal (RS) transmission for detection of
coherent of a PUCCH) which can be used for control information
transmission.
[0141] In 3GPP LTE, a PUCCH is defined in seven different formats
according to transmitted control information, modulation scheme and
the quantity of control information and attributes of transmitted
uplink control information (UCI) according to each PUCCH format can
be summarized as shown in Table 2.
TABLE-US-00002 TABLE 2 Number of PUCCH Modulation bits per format
scheme subframe Usage etc. 1 N/A N/A SR (Scheduling Request) 1a
BPSK 1 ACK/NACK One codeword 1b QPSK 2 ACK/NACK Two codeword 2 QPSK
20 CQI Joint Coding ACK/NACK (extended CP) 2a QPSK + BPSK 21 CQI +
ACK/ Normal CP only NACK 2b QPSK + BPSK 22 CQI + ACK/ Normal CP
only NACK
[0142] PUCCH format 1 is used to transmit an SR only. When the SR
is solely transmitted, an unmodulated waveform is applied, which
will be described in detail below.
[0143] PUCCH format la or lb is used for HARQ ACK/NACK
transmission. When HARQ ACK/NACK is solely transmitted in a
subframe, PUCCH format la or lb may be used. Furthermore, HARQ
ACK/NACK and SR may be transmitted in the same subframe using PUCCH
format la or lb.
[0144] PUCCH format 2 is used for CQI transmission whereas PUCCH
format 2a or 2b is used for transmission of CQI and HARQ ACK/NACK.
In the extended CP case, PUCCH format 2 may be used for
transmission of CQI and HARQ ACK/NACK.
[0145] FIG. 6 illustrates mapping of PUCCH formats to PUCCH regions
in uplink physical resource blocks. In FIG. 6, N.sub.RB.sup.UL
denotes the number of resource blocks on uplink and 0, 1, . . . ,
N.sub.RB.sup.UL-1 denote physical resource block numbers. PUCCHs
are mapped to both edges of uplink frequency blocks basically. As
shown in FIG. 6, PUCCH formats 2/2a/2b are mapped to PUCCH regions
indicated by m=0,1, which represents that PUCCH formats 2/2a/2b are
mapped to resource blocks located at band-edges. PUCCH formats
2/2a/2b and PUCCH formats 1/1a/lb may be mixed and mapped to PUCCH
regions indicated by m=2. PUCCH formats 1/1a/1b may be mapped to
PUCCH regions indicated by m=3,4,5. The number RB of PUCCH RBs can
be used by PUCCH formats 2/2a/2b may be signaled to UEs in a cell
through broadcasting signaling.
[0146] PUCCH Resource
[0147] A BS allocates a PUCCH resource for UCI transmission to a UE
using an explicit or implicit method through higher layer
signaling.
[0148] In the case of ACK/NACK, a plurality of PUCCH resource
candidates may be set for a UE by a higher layer and a PUCCH
resource to be used by the UE from among the PUCCH resource
candidates may be implicitly determined. For example, the UE can
receive a PDSCH from the BS and transmit ACK/NACK for a
corresponding to data unit through a PUCCH resource implicitly
indicated by a PDCCH resource carrying scheduling information on
the PDSCH.
[0149] In LTE, a PUCCH resource that will carry ACK/NACK
information is not previously allocated to a UE. Rather, plural
PUCCH resources are used separately at each time instant plural UEs
within a cell. Specifically, a PUCCH resource that a UE will use to
transmit ACK/NACK information is implicitly indicated by a PDCCH
carrying scheduling information for a PDSCH that delivers downlink
data. An entire area carrying PDCCHs in a DL subframe include a
plurality of Control Channel Elements (CCEs) and a PDCCH
transmitted to a UE includes one or more CCEs. A CCE includes a
plurality of (e.g. 9) Resource Element Groups (REGs). One REG
includes four contiguous REs except for an RS. The UE transmits
ACK/NACK information on an implicit PUCCH that is derived or
calculated by a function of a specific CCE index (e.g. the first or
lowest CCE index) from among the indexes of CCEs included in a
received PDCCH. That is, each PUCCH resource index can correspond
to a PUCCH resource for ACK/NACK. For example, if a PDCCH including
CCEs #4, #5 and #6 delivers scheduling information on a PDSCH to a
UE, the UE transmits ACK/NACK information to a BS on a PUCCH, for
example, PUCCH #4 derived or calculated using the lowest CCE index
of the PDCCH, CCE index 4. Up to M' CCEs may be present in a
downlink subframe and up to M PUCCHs may be present in an uplink
subframe. Although M may be equal to M', M may be different from M'
and CCEs may be mapped to PUCCHs in an overlapping manner.
[0150] For instance, a PUCCH resource index may be calculated by
the following equation.
n.sup.(1).sub.PUCCH=n.sub.CCE+N.sup.(1).sub.PUCCH [Equation 15]
[0151] Here, n.sup.(1).sub.PUCCH denotes the index of a PUCCH
resource for transmitting ACK/NACK information, N.sup.(1).sub.PUCCH
denotes a signaling value received from a higher layer, and
n.sub.CCE denotes the lowest of CCE indexes used for transmission
of a PDCCH.
[0152] PUCCH Channel Structure
[0153] PUCCH formats 1a and 1b are described.
[0154] In the PUCCH format la/lb, a symbol modulated using BPSK or
QPSK is multiplied by a CAZAC sequence of length 12. For example,
when a modulated symbol d(0) is multiplied by a length-N CAZAC
sequence r(n) (n=0, 1, 2, . . . , N-1), y(0), y(1), y(2), y(N-1)
are obtained. Symbols y(0), y(1), y(2), . . . , y(N-1) may be
called a block of symbols. Upon completion of the CAZAC sequence
multiplication, the resultant symbol is blockwise-spread using an
orthogonal sequence.
[0155] A Hadamard sequence of length 4 is applied to general
ACK/NACK information, and a DFT (Discrete Fourier Transform)
sequence of length 3 is applied to shortened ACK/NACK information
and a reference signal. A Hadamard sequence of length 2 may be
applied to the reference signal in the case of the extended CP.
[0156] FIG. 7 illustrates an ACK/NACK channel structure in normal
CP case. FIG. 7 shows an exemplary PUCCH channel structure for HARQ
ACK/NACK transmission without CQI. Three contiguous SC-FDMA symbols
in the middle of seven SC-FDMA symbols carry an RS and the
remaining four SC-FDMA symbols carry an ACK/NACK signal. In the
case of the extended CP, two contiguous symbols in the middle of
SC-FDMA symbols may carry an RS. The number and positions of
symbols used for the RS may depend on a control channel and the
number and positions of symbols used for the ACK/NACK signal may be
changed according to the number and positions of symbols used for
the RS.
[0157] 1-bit ACK/NACK information and 2-bit ACK/NACK information
(unscrambled) may be represented a HARQ ACK/NACK modulation symbol
using BPSK and QPSK, respectively. ACK information may be encoded
as 1' and NACK information may be encoded as `0`.
[0158] When a control signal is transmitted in an allocated band,
2-dimensional spreading is applied to improve multiplexing
capacity. That is, frequency domain spreading and time domain
spreading are simultaneously applied to increase the number of UEs
or control channels that can be multiplexed. To spread an ACK/NACK
signal in the frequency domain, a frequency domain sequence is used
as a basic sequence. A Zadoff-Chu (ZC) sequence, one type of CAZAC
sequence, can be used as the frequency domain sequence. For
example, different cyclic shifts (CSs) can be applied to a ZC
sequence as a basic sequence to multiple different UEs or different
control channels. The number of CS resources supported by SC-FDMA
symbols for PUCCH RBs for HARQ ACK/NACK transmission is set by a
cell-specific higher-layer signaling parameter
.DELTA..sub.shift.sup.PUCCH and .DELTA..sub.shift.sup.PUCCH
.di-elect cons. {1, 2, 3} represents 12, 6 or 4 shifts.
[0159] The frequency-domain-spread ACK/NACK signal is spread in the
time domain using an orthogonal spreading code. A Walsh-Hadamard
sequence or a DFT sequence can be used as the orthogonal spreading
code. For example, an ACK/NACK signal can be spread using a
length-4 orthogonal sequence w0, w1, w2, w3. An RS is spread using
a length-2 or length-2 orthogonal sequence. This is called
orthogonal covering.
[0160] A plurality of UEs can be multiplexed through code division
multiplexing (CDM) using CS resources in the frequency domain and
OC resources in the time domain as described above. That is,
ACK/NACK information and RSs of a large number of UEs can be
multiplexed on the same PUCCH RB.
[0161] For time domain spreading CDM, the number of spreading codes
supported for ACK/NACK information is limited by the number of RS
symbols. That is, since the number of SC-FDMA symbols for RS
transmission is smaller than the number of SC-FDMA symbols for
ACK/NACK transmission, multiplexing capacity of an RS is less than
multiplexing capacity of ACK/NACK information. For example, while
ACK/NACK information can be transmitted through four symbols in the
normal CP case, three orthogonal spreading codes are used for
ACK/NACK information because the number of RS transmission symbols
is limited to three and thus only three orthogonal spreading codes
can be used for the RS.
[0162] Examples of an orthogonal sequence used to spread ACK/NACK
information are shown in Tables 3 and 4. Table 3 shows a sequence
for a length-4 symbol and Table 4 shows a sequence for a length-3
symbol. The sequence for the length-4 symbol is used in PUCCH
format 1/la/lb of a normal subframe configuration. Considering a
case in which an SRS is transmitted on the last symbol of the
second slot in a subframe configuration, the sequence for the
length-4 symbol can be applied to the first slot and shortened
PUCCH format 1/1a/lb of the sequence for the length-3 symbol can be
applied to the second slot.
TABLE-US-00003 TABLE 3 Sequence index [w(0), w(1), w(2), w(3)] 0
[+1 +1 +1 +1] 1 [+1 -1 +1 -1] 2 [+1 -1 -1 +1]
TABLE-US-00004 TABLE 4 Sequence index [w(0), w(1), w(2)] 1 [1 1 1]
1 [1 e.sup.j2.pi./3 e.sup.j4.pi./3] 2 [1 e.sup.j4.pi./3
e.sup.j2.pi./3]
[0163] An exemplary orthogonal sequence used for RS spreading of an
ACK/NACK channel is as shown in Table 5.
TABLE-US-00005 TABLE 5 Sequence index Normal CP Extended CP 0 [1 1
1] [1 1] 1 [1 e.sup.j2.pi./3 e.sup.j4.pi./3] [1 -1] 2 [1
e.sup.j4.pi./3 e.sup.j2.pi./3] N/A
[0164] When three symbols are used for RS transmission and four
symbols are used for ACK/NACK information transmission in a slot of
a normal CP subframe, if six CSs in the frequency domain and three
OC resources in the time domain can be used, for example, HARQ
ACK/NACK signals from a total of 18 different UEs can be
multiplexed in a PUCCH RB. When two symbols are used for RS
transmission and four symbols are used for ACK/NACK information
transmission in a slot of an extended CP subframe, if six CSs in
the frequency domain and two OC resources in the time domain can be
used, for example, HARQ ACK/NACK signals from a total of 12
different UEs can be multiplexed in a PUCCH RB.
[0165] PUCCH format 1 is described. A UE requests scheduling
through a scheduling request (SR). An SR channel reuses an ACK/NACK
channel structure in the PUCCH format la/lb and is configured in an
on-off keying manner on the basis of ACK/NACK channel design. A
reference signal is not transmitted on the SR channel. Accordingly,
a length-7 sequence is used in the normal CP case and a length-6
sequence is used in the extended CP case. Different CSs or
orthogonal covers may be allocated to an SR and ACK/NACK. That is,
for positive SR transmission, a UE transmits HARQ ACK/NACK through
a resource allocated for the SR. For negative SR transmission, the
UE transmits HARQ ACK/NACK through a resource allocated for
ACK/NACK.
[0166] The PUCCH format 2/2a/2b is will now be described. The PUCCH
format 2/2a/2b is used to transmit channel measurement feedback
(CQI, PMI and RI).
[0167] A channel feedback (referred to as CQI hereinafter)
reporting period and a frequency unit (or frequency resolution)
corresponding to a measurement target can be controlled by an eNB.
Periodic and aperiodic CQI reports can be supported in the time
domain. PUCCH format 2 can be used for the periodic report only and
a PUSCH can be used for the aperiodic report. In the case of
aperiodic report, the eNB can instruct a UE to transmit an
individual CQI report on a resource scheduled to transmit uplink
data.
[0168] FIG. 8 illustrates a CQI channel structure in the case of
normal CP. SC-FDMA symbols #1 to #5 (second and sixth symbols) from
among SC-FDMA symbols #0 to #6 of a slot can be used for DMRS
transmission and the remaining SC-FDMA symbols can be used for CQI
transmission. In the case of extended CP, an SC-FDMA symbol
(SC-FDMA symbol #3) is used for DMRS transmission.
[0169] The PUCCH format 2/2a/2b supports modulation by a CAZAC
sequence and a symbol modulated according to QPSK is multiplied by
a CAZAC sequence of length 12. A CS of the sequence is changed
between symbols and between slots. Orthogonal covering is used for
the DMRS.
[0170] Two SC-FDMA symbols having a distance therebetween, which
corresponds to the interval of three SC-FDMA symbols, from among
seven SC-FDMA symbols included in a slot carry a DMRS and the
remaining five SC-FDMA symbols carry CQI. Two RSs are used in a
slot in order to support a fast UE. Each UE is identified using a
CS sequence. CQI symbols are modulated into SC-FDMA symbols and
transmitted. The SC-FDMA symbols are composed of a sequence. That
is, a UE modulates CQI into each sequence and transmits the
sequence.
[0171] The number of symbols that can be transmitted in a TTI is 10
and modulation of CQI is performed using QPSK. When QPSK mapping is
used for SC-FDMA symbols, an SC-FDMA symbol can carry 2-bit CQI and
thus a slot can carry 10-bit CQI. Accordingly, a maximum of 20-bit
CQI can be transmitted in a subframe. To spread CQI in the
frequency domain, a frequency domain spreading code is used.
[0172] A length-12 CAZAC sequence (e.g. ZC sequence) can be used as
the frequency domain spreading code. Control channels can be
discriminated from each other using CAZAC sequences having
different CS values. The frequency-domain-spread CQI is subjected
to IFFT.
[0173] 12 different UEs can be orthogonally multiplexed in the same
PUCCH RB using 12 CSs at an equal interval. In the case of normal
CP, while a DMRS sequence on SC-FDMA symbols #1 and #5 (SC-FDMA
symbols #3 in the case of extended CP) is similar to a CQI signal
sequence in the frequency domain, the DMRS sequence is not
modulated. A UE can be semi-statically configured by higher layer
signaling to periodically report different CQI, PMI and RI types on
a PUCCH resource indicated by a PUCCh resource index
n.sub.PUCCH.sup.(2). Here, the PUCCH resource index
n.sub.PUCCH.sup.(2) is information indicating a PUCCH region and a
CS value used for PUCCH format 2/2a/2b transmission.
[0174] An enhanced PUCCH (e-PUCCH) format will now be described.
The e-PUCCH format may correspond to the PUCCH format 3 of LTE-A.
Block spreading can be applied to ACK/NACK transmission using PUCCH
format 3.
[0175] Block spreading is a method of modulating a control signal
using SC-FDMA, distinguished from the PUCCH format 1 series or 2
series. As shown in FIG. 13, a symbol sequence can be spread in the
time domain using an orthogonal cover code (OCC) and transmitted.
Control signals of plural UEs can be multiplexed in the same RB
using the OCC. A symbol sequence is transmitted in the time domain
and control signals of multiple UEs are multiplexed using CSs of a
CAZAC sequence in the above-described PUCCH format 2, whereas a
symbol sequence is transmitted in the frequency domain and control
signals of multiple UEs are multiplexed through time domain
spreading using an OCC in the block spreading based PUCCH format
(e.g. PUCCH format 3).
[0176] FIG. 9(a) illustrates an example of generating and
transmitting four SC-FDMA symbols (i.e. data part) using a length-4
(or spreading factor (SF)=4) OCC in a symbol sequence during one
slot. In this case, three RS symbols (i.e. RS part) can be used in
one slot.
[0177] FIG. 9(b) illustrates an example of generating and
transmitting five SC-FDMA symbols (i.e. data part) using a length-5
(or SF=5) OCC in a symbol sequence during one slot. In this case,
two RS symbols can be used per slot.
[0178] In the examples of FIG. 9, the RS symbols can be generated
from a CAZAC sequence to which a specific CS value is applied, and
a predetermined OCC can be applied to (or multiplied by) a
plurality of RS symbols and transmitted. If 12 modulated symbols
are used per OFDM symbol (or SC-FDMA symbol) and each modulated
symbol is generated according to QPSK in the example of FIG. 13, a
maximum of 12.times.2=24 bits can be transmitted in a slot.
Accordingly, a total of 48 bits can be transmitted in two slots.
When a block spreading based PUCCH channel structure is used as
described above, it is possible to transmit an increased quantity
of control information compared to the PUCCH format 1 series and 2
series.
[0179] Carrier Aggregation
[0180] The concept of a cell, which is introduced to manage radio
resources in LTE-A is described prior to carrier aggregation (CA).
A cell may be regarded as a combination of downlink resources and
uplink resources. The uplink resources are not essential elements,
and thus the cell may be composed of the downlink resources only or
both the downlink resources and uplink resources. This is
definition in LTE-A release 10, and the cell may be composed of the
uplink resources only. The downlink resources may be referred to as
downlink component carriers and the uplink resources may be
referred to as uplink component carriers. A DL CC and a UL CC may
be represented by carrier frequencies. A carrier frequency means a
center frequency in a cell.
[0181] Cells may be divided into a primary cell (PCell) operating
at a primary frequency and a secondary cell (SCell) operating at a
secondary frequency. The PCell and SCell may be collectively
referred to as serving cells. The PCell may be designated during an
initial connection establishment, connection re-establishment or
handover procedure of a UE. That is, the PCell may be regarded as a
main cell relating to control in a CA environment. A UE may be
allocated a PUCCH and transmit the PUCCH in the PCell thereof. The
SCell may be configured after radio resource control (RRC)
connection establishment and used to provide additional radio
resources. Serving cells other than the PCell in a CA environment
may be regarded as SCell. For a UE in an RRC connected state for
which CA is not established or a UE that does not support CA, only
one serving cell composed of the PCell is present. For a UE in the
RRC-connected state for which CA is established, one or more
serving cells are present and the serving cells include a PCell and
SCells. For a UE that supports CA, a network may configure one or
more SCell in addition to a PCell initially configured during
connection establishment after initial security activation is
initiated.
[0182] CA is described with reference to FIG. 10. CA is a
technology introduced to use a wider band to meet demands for a
high transmission rate. CA can be defined as aggregation of two or
more component carriers (CCs) having different carrier frequencies.
FIG. 10(a) shows a subframe when a conventional LTE system uses a
single CC and FIG. 8(b) shows a subframe when CA is used. In FIG.
10(b), 3 CCs each having 20 MHz are used to support a bandwidth of
60 MHz. The CCs may be contiguous or non-contiguous.
[0183] A UE may simultaneously receive and monitor downlink data
through a plurality of DL CCs. Linkage between a DL CC and a UL CC
may be indicated by system information. DL CC/UL CC linkage may be
fixed to a system or semi-statically configured. Even when a system
bandwidth is configured of N CCs, a frequency bandwidth that can be
monitored/received by a specific UE may be limited to M (<N)
CCs. Various parameters for CA may be configured cell-specifically,
UE group-specifically, or UE-specifically.
[0184] FIG. 11 is a diagram illustrating cross-carrier scheduling.
Cross carrier scheduling is scheme by which a control region of one
of DL CCs of a plurality of serving cells includes downlink
scheduling allocation information the other DL CCs or a scheme by
which a control region of one of DL CCs of a plurality of serving
cells includes uplink scheduling grant information about a
plurality of UL CCs linked with the DL CC.
[0185] A carrier indicator field (CIF) is described first. The CIF
may be included in a DCI format transmitted through a PDCCH or not.
When the CIF is included in the DCI format, this represents that
cross carrier scheduling is applied. When cross carrier scheduling
is not applied, downlink scheduling allocation information is valid
on a DL CC currently carrying the downlink scheduling allocation
information. Uplink scheduling grant is valid on a UL CC linked
with a DL CC carrying downlink scheduling allocation
information.
[0186] When cross carrier scheduling is applied, the CIF indicates
a CC associated with downlink scheduling allocation information
transmitted on a DL CC through a PDCCH. For example, referring to
FIG. 9, downlink allocation information for DL CC B and DL CC C,
that is, information about PDSCH resources is transmitted through a
PDCCH in a control region of DL CC A. A UE can recognize PDSCH
resource regions and the corresponding CCs through the CIF by
monitoring DL CC A.
[0187] Whether or not the CIF is included in a PDCCH may be
semi-statically set and UE-specifically enabled according to higher
layer signaling.
[0188] When the CIF is disabled, a PDCCH on a specific DL CC may
allocate a PDSCH resource on the same DL CC and assign a PUSCH
resource on a UL CC linked with the specific DL CC. In this case,
the same coding scheme, CCE based resource mapping and DCI formats
as those used for the conventional PDCCH structure are
applicable.
[0189] When the CIF is enabled, a PDCCH on a specific DL CC may
allocate a PDSCH/PUSCH resource on a DL/UL CC indicated by the CIF
from among aggregated CCs. In this case, the CIF can be
additionally defined in existing PDCCH DCI formats. The CIF may be
defined as a field having a fixed 3-bit length, or a CIF position
may be fixed irrespective of DCI format size. In this case, the
same coding scheme, CCE based resource mapping and DCI formats as
those used for the conventional PDCCH structure are applicable.
[0190] Even when the CIF is present, an eNB can allocate a DL CC
set through which a PDCCH is monitored. Accordingly, blinding
decoding overhead of a UE can be reduced. A PDCCH monitoring CC set
is part of aggregated DL CCs and a UE can perform PDCCH
detection/decoding in the CC set only. That is, the eNB can
transmit the PDCCH only on the PDCCH monitoring CC set in order to
schedule a PDSCH/PUSCH for the UE. The PDCCH monitoring DL CC set
may be configured UE-specifically, UE group-specifically or
cell-specifically. For example, when 3 DL CCs are aggregated as
shown in FIG. 9, DL CC A can be configured as a PDCCH monitoring DL
CC. When the CIF is disabled, a PDCCH on each DL CC can schedule
only the PDSCH on DL CC A. When the CIF is enabled, the PDCCH on DL
CC A can schedule PDSCHs in other DL CCs as well as the PDSCH in DL
CC A. When DL CC A is set as a PDCCH monitoring CC, DL CC B and DL
CC C do not transmit PDSCHs.
[0191] ACK/NACK Transmission
[0192] In a system to which the aforementioned CA is applied, a UE
can receive a plurality of PDSCHs through a plurality of downlink
carriers. In this case, the UE should transmit ACK/NACK for data on
a UL CC in a subframe. When a plurality of ACK/NACK signals is
transmitted in a subframe using PUCCH format la/lb, high transmit
power is needed, a PAPR of uplink transmission increases and a
transmission distance of the UE from the eNB may decrease due to
inefficient use of a transmit power amplifier. To transmit a
plurality of ACK/NACK signals through a PUCCH, ACK/NACK bundling or
ACK/NACK multiplexing may be employed.
[0193] There may be generated a case in which ACK/NACK information
for a large amount of downlink data according to application of CA
and/or a large amount of downlink data transmitted in a plurality
of DL subframes in a TDD system needs to be transmitted through a
PUCCH in a subframe. In this case, the ACK/NACK information cannot
be successfully transmitted using the above-mentioned ACK/NACK
bundling or multiplexing when the number of ACK/NACK bits to be
transmitted is greater than the number of ACK/NACK bits that can be
supported by ACK/NACK bundling or multiplexing.
[0194] An ACK/NACK multiplexing scheme will now be described.
[0195] In case of ACK/NACK multiplexing, the contents of an
ACK/NACK response to a plurality of data units can be identified by
a combination of an ACK/NACK unit actually used for ACK/NACK
transmission and symbols modulated according to QPSK. For example,
if an ACK/NACK unit carries 2-bit information and receives a
maximum of two data units and a HARQ ACK/NACK response to each of
the received data units is represented by an ACK/NACK bit, a
transmitter that has transmitted data can identify ACK/NACK results
as shown in Table 6.
TABLE-US-00006 TABLE 6 HARQ-ACK(0), HARQ-ACK(1) n.sub.PUCCH.sup.(1)
b(0), b(1) ACK, ACK n.sub.PUCCH,1.sup.(1) 1, 1 ACK, NACK/DTX
n.sub.PUCCH,0.sup.(1) 0, 1 NACK/DTX, ACK n.sub.PUCCH,1.sup.(1) 0, 0
NACK/DTX, NACK n.sub.PUCCH,1.sup.(1) 1, 0 NACK, DTX
n.sub.PUCCH,0.sup.(1) 1, 0 DTX, DTX N/A N/A
[0196] In Table 6, HARQ-ACK(i) (i=0, 1) represents an ACK/NACK
result with respect to data unit i. Since a maximum of two data
units (data unit 0 and data unit 1) are received as described
above, an ACK/NACK result with respect to data unit 0 is
represented as HARQ-ACK(0) and an ACK/NACK result with respect to
data unit 1 is represented as HARQ-ACK(1) in Table 6. DTX
(Discontinuous Transmission) indicates that the data unit
corresponding to HARQ-ACK(i) is not transmitted or a receiver
cannot detect the data unit corresponding to HARQ-ACK(i). In Table
6, n.sub.PUCCH,X.sup.(1) denotes an ACK/NACK unit used for actual
ACK/NACK transmission. When a maximum of two ACK/NACK units are
present, the ACK/NACK units can be represented as
n.sub.PUCCH,0.sup.(1) and n.sub.PUCCH,1.sup.(1). In addition, b(0)
and b(1) denote two bits transmitted by selected ACK/NACK units.
Modulated symbols transmitted through ACK/NACK units are determined
based on b(0) and b(1).
[0197] For example, when the receiver successfully receives and
decodes two data units (in the case of ACK and ACK of Table 6), the
receiver transmits two bits (1, 1) using the ACK/NACK unit
n.sub.PUCCH,1.sup.(1). If the receiver receives two data units,
fails to decode (or detect) the first data unit (i.e. data unit 0
corresponding to HARQ-ACK(0)) and successfully decodes the second
data unit (i.e. data unit 1 corresponding to HARQ-ACK(1)) (in the
case of NACK/DTX and ACK of Table 6), the receiver transmits two
bits (0, 0) using the ACK/NACK unit n.sub.PUCCH,1.sup.(1).
[0198] As described above, it is possible to transmit ACK/NACK
information about a plurality of data units using a single ACK/NACK
unit by linking or mapping a combination of a selected ACK/NACK
unit and bits of the selected ACK/NACK unit (i.e. a combination of
n.sub.PUCCH,0.sup.(1) or n.sub.PUCCH,1.sup.(1) and b(0) and b(1) in
FIG. 6) to the contents of ACK/NACK. ACK/NACK multiplexing for two
or more data units can be easily implemented by extending the
principle of the above-described ACK/NACK multiplexing.
[0199] In the above-described ACK/NACK multiplexing scheme, NACK
and DTX may not be discriminated from each other when one or more
ACKs are present for each data unit (that is, NACK and DTX can be
coupled as NACK/DTX as shown in Table 6). This is because all
ACK/NACK states (i.e. ACK/NACK hypotheses) that may be generated
when NACK and DTX are discriminated from each other cannot be
represented by only combinations of ACK/NACK units and symbols
modulated by BPSK. When ACK is not present for any data unit (that
is, only NACK or DTX is present for all data units), a single
definite NACK case that represents a definite NACK (NACK
discriminated from DTX) from among HARQ-ACK(i) can be defined. In
this case, a PUCCH resource corresponding to a data unit with
respect to a definite NACK may be reserved to transmit a plurality
of ACK/NACK signals.
[0200] D2D Communication
[0201] A description will be given of a D2D communication scheme
when D2D communication is introduced to a wireless communication
system (e.g. 3GPP LTE system or 3GPP LTE-A system).
[0202] FIG. 12 illustrates the concept of D2D communication. FIG.
12(a) shows a conventional BS based communication scheme through
which UE1 transmits data to a BS on uplink and the BS transmits the
data from UE1 to UE2 on downlink.
[0203] FIG. 12(b) illustrates a UE-to-UE communication scheme as an
exemplary D2D communication scheme, through which data can be
exchanged between UEs without a BS. A link directly established
between devices may be called a D2D link. D2D communication reduces
latency and requires a smaller quantity of radio resources,
compared to conventional BS based communication.
[0204] While D2D communication supports communication between
devices (or between UEs) without a BS, D2D communication must not
cause interference or disturbance in a legacy wireless
communication network because D2D communication is performed by
reusing resources of the legacy wireless communication network
(e.g. 3GPP LTE or 3GPP LTE-A). That is, resources for D2D
communication need to be allocated by a BS although data is
transmitted/received between devices without the BS. Accordingly,
the present invention proposes a method of allocating resources for
D2D communication by a BS. For example, uplink resources can be
reused as resources for D2D communication.
[0205] A description will be given of a D2D communication procedure
on the assumption that UE1 and UE2 directly communicate with each
other without an eNB. While direct communication between UEs is
exemplified as the D2D communication scheme proposed by the present
invention for clarity of description, the scope of the present
invention is not limited thereto. That is, the technical spirit of
the present invention is applicable to D2D communication in a broad
sense. For example, the D2D communication scheme of the present
invention can be applied to operation of an eNB to transmit a
signal to a UE using resources set through uplink by a cell to
which the eNB belongs or a neighboring cell. Specifically, it is
possible to equally apply the principle of the D2D communication
scheme proposed by the present invention to communication between
an eNB and a UE by considering the eNB as a UE that transmits a
signal through an uplink resource.
[0206] FIG. 13 is a flowchart illustrating an exemplary D2D
communication method according to the present invention. All or
some steps of the D2D communication method illustrated in FIG. 13
may implement embodiments of the present invention. That is,
essential components of the present invention need not include the
entire procedure illustrated in FIG. 13 and only part of the
procedure may be regarded as essential elements for accomplishing
the object of the present invention. Embodiments of the present
invention will be described according to process flow for
clarity.
[0207] The following embodiment is described on the assumption that
UE1 transmits data and UE2 receives data in D2D communication in
FIG. 13.
[0208] 1. D2D Communication Resource Request
[0209] A UE participating in D2D communication may request an eNB
to provide a resource for D2D communication through steps S1310,
S1320 and S1330.
[0210] In step S1310, UE2 that wants to transmit data to UE2 in a
D2D communication manner requests the eNB to allocate a resource
for D2D communication to UE1. The eNB may transmit an uplink grant
to UE1 in response to the request of UE1 in step S1320. In step
S1330, UE1 may transmit information related to D2D communication to
the eNB using the uplink grant received in step S1320. In normal
wireless communication systems, an uplink grant may refer to
scheduling information for uplink transmission from a UE to an
eNB.
[0211] The uplink grant in step S1320 is scheduling information
used for a UE to transmit information related to D2D communication
to the eNB. Specifically, the resource allocation request in step
S1310 corresponds to request control information used for UE1 to
request the eNB to provide uplink transmission opportunity to UE1
when UE1 is not allocated a resource for uplink transmission by the
eNB. Since U1 that is not allocated the resource to uplink
transmission cannot transmit a large quantity of information to the
eNB, UE1 may transmit D2D communication related information to the
eNB through steps S1310, S1320 and S1330 and request the eNB to
allocate a resource for D2D thereto.
[0212] More specifically, control information for a D2D
communication resource allocation request transmitted from UE1 in
step S1310 may be a scheduling request (SR) or physical random
access channel (PRACH) preamble. The SR is control information for
requesting allocation of a resource available for uplink
transmission. The PRACH preamble may be transmitted to an eNB at an
arbitrary time in a random access procedure while a UE is not
allocated a resource for uplink transmission. The eNB provides a UL
grant to the UE in response to the PRACH preamble. Accordingly, in
the present embodiment of the invention, UE1 may transmit the SR or
PRACH preamble to the eNB in order to obtain uplink transmission
opportunity to transmit detailed information for D2D communication.
In addition to the SR and PRACH preamble, a predetermined indicator
or control information indicating that UE1 requests D2D
communication resource allocation may be transmitted in step
S1310.
[0213] Information transmitted from UE1 to the eNB in step S1330
may include an indicator indicating a request for D2D
communication, IDs of devices (e.g., UE1 and UE2) participating in
D2D communication, a buffer status report (BSR) on the quantity of
data traffic to be transmitted through D2D communication, which is
accumulated in a buffer of UE1, etc. Upon reception of this
information, the eNB may specify devices paired for D2D
communication and determine the quantity of resources necessary for
D2D communication.
[0214] If UE1 has obtained uplink transmission opportunity from the
eNB prior to step S1310, steps S1310 and S1320 may be omitted and
detailed information about D2D communication may be transmitted
along with the control information for requesting D2D communication
resource allocation in step S1330.
[0215] 2. D2D Link Detection
[0216] Parameters (e.g. transmit power, modulation and coding
scheme (MCS), etc.) of D2D communication for a link between UE1 and
UE2 can be determined by the eNB. Accordingly, communication
performed by devices in a legacy wireless communication system is
not affected by D2D communication.
[0217] To enable the eNB to recognize a D2D communication link
state, a device participating in D2D communication may report a
channel state of a D2D link to the eNB. To achieve this, the eNB
may instruct UE1 to transmit a predetermined signal detectable by
UE2 and instruct UE2 to report the strength or quality of the
signal received from UE1 to the eNB. Accordingly, UE1 can transmit
a signal for D2D link detection to UE2 (S1340) and UE2 can report a
D2D link detection result (e.g. an SINR or MCS level) to the eNB
(S1350), as shown in FIG. 13.
[0218] Instructions of the eNB to perform steps S1340 and S1350 may
be transmitted to UE1 and UE2 through explicit signaling (not
shown) or in an implicit manner. Otherwise, steps S1340 and S1350
may be performed according to a rule predetermined for D2D link
detection signal transmission.
[0219] Specifically, the signal transmitted by UE1 in step S1340
may be a periodic or aperiodic SRS transmitted on an uplink
resource. In the case of SRS, the eNB can control UE1 to transmit
an SRS sequence set by the eNB at a timing determined by the eNB
through a resource determined by the eNB by transmitting an
appropriate SRS configuration to UE1.
[0220] In addition, the eNB can enable UE2 to easily detect the SRS
transmitted from UE1 by signaling the SRS configuration to UE2
through higher layer signaling (e.g. RRC signaling). That is, UE2
can attempt to detect the signal (e.g. a specific sequence) from
UE1 on the uplink resource corresponding to the SRS configuration
for UE1, signaled by the eNB.
[0221] Furthermore, the predetermined signal transmitted by UE1 in
step S1340 may be a PRACH preamble for random access, for example.
The PRACH preamble occupies a narrower bandwidth than the SRS, and
thus UE2 can easily detect the signal from UE1 using a smaller
quantity of frequency resource.
[0222] The eNB can enable UE2 to easily detect the PRACH preamble
transmitted from UE1 by signaling information about the PRACH
preamble to UE2 through higher layer signaling (e.g. RRC
signaling).
[0223] The PRACH preamble transmitted from UE1 in step S1340 may be
used by UEs that attempt initial access. Resources other than the
PRACH preamble may be used. For example, the eNB can instruct UE1
to use a PRACH resource reserved for handover as a D2D link
detection signal.
[0224] The eNB may instruct UE1 to periodically transmit a specific
PRACH preamble in order to prepare for a case in which UE2 cannot
successfully detect the signal from UE 1.
[0225] In addition, the signal (e.g. SRS or PRACH preamble)
transmitted by UE1 in step S1340 may be
UE1-specifically-randomized. For example, the sequence of the
signal transmitted by UE1 can be randomized based on the ID of UE1.
In this case, the eNB may signal the ID of UE1 to UE2 such that UE2
can detect the signal from UE1 more easily.
[0226] UE2 can report the result of detection of the signal from
UE1 to the eNB in step S1350. The eNB can recognize channel
characteristics of the D2D link between UE1 and UE2 based on the
report from UE2 and acquire synchronization of the link between UE1
and UE2.
[0227] 3. D2D Communication Resource Allocation
[0228] The eNB can allocate resources for D2D communication to
devices participating in D2D communication. For example, the eNB
can transmit scheduling information for D2D communication to UE1
and UE2, as shown in steps S1360 and S1370 of FIG. 13. Steps S1360
and S1370 may be performed simultaneously or at different times.
The D2D communication scheduling information may be determined on
the basis of the D2D communication related information (information
on devices participating in D2D communication, information on a
link to be used for D2D communication, etc.) acquired by the eNB
through steps S1330 and/or S1350. If some of the devices
participating in D2D communication are served by a neighboring
cell, the D2D communication scheduling information may be
determined in consideration of scheduling information with respect
to the neighboring cell (i.e. according to inter-cell cooperation)
and the neighboring cell may provide the scheduling information to
the corresponding devices.
[0229] The D2D communication scheduling information received by UE1
in step S1360 may be regarded as a UL grant from the viewpoint of
UE1 corresponding to a device transmitting data in D2D
communication. That is, operation of UE1 to perform uplink
transmission through an uplink resource designated by the D2D
communication scheduling information from the eNB can be considered
similar to operation of a UE to perform uplink transmission
according to a UL grant from an eNB in conventional wireless
communication systems. Accordingly, the conventional uplink
transmission operation according to a UL grant can be reused for
UE1 corresponding to a device transmitting data in D2D
communication.
[0230] The D2D communication scheduling information received by UE2
in step S1370 needs to be interpreted as information for
instructing reception operation to be performed on an uplink
resource from the viewpoint of UE2 corresponding to a device
receiving data in D2D communication. While only uplink transmission
or downlink reception operation is defined for UEs in conventional
wireless communication systems, uplink reception operation is
defined for UEs in D2D communication according to the present
invention.
[0231] For example, the eNB can represent whether a UL grant
indicates transmission operation or reception operation of a UE
using a specific field of the UL grant. To achieve this, only one
bit is needed and thus a bit reserved in a specific field of a
conventional UL grant can be used. Otherwise, a new field
indicating transmission or reception operation using a UL grant may
be defined.
[0232] Alternatively, devices participating in D2D communication
may have additional IDs solely for D2D communication in addition to
IDs used for communication with the eNB and a UL grant transmitted
(e.g., masked with a corresponding RNTI) for the IDs for D2D
communication may be construed as a signal indicating uplink
reception operation. For example, UE1 may have ID_UE1_cell for
communication with the eNB and ID_UE1_D2D for D2D communication and
UE2 may have ID_UE2_cell for communication with the eNB and
ID_UE2_D2D for D2D communication. The eNB may transmit a UL grant
for ID_UE1_cell (S1360) to UE1 that transmits data in D2D
communication because the eNB needs to instruct UE1 to perform
operation similar to normal operation according to a UL grant and
transmit a UL grant for ID_UE2_D2D to UE2 that receives data in D2D
communication (S1370).
[0233] Alternatively, downlink assignment information may be
transmitted to UE2 (device receiving data in D2D communication) in
step S1370. In conventional wireless communication systems, DL
assignment information may be scheduling information for downlink
transmission from an eNB to a UE. The DL assignment information
used in step S1370 may be new DL assignment information for
instructing UE2 to perform reception using an uplink resource
instead of a downlink resource. The new DL assignment information
may include a specific field indicating whether the DL assignment
information instructs UE2 to perform uplink reception operation or
downlink reception operation, for example. Here, the specific field
may use a bit reserved in a specific field of the conventional DL
assignment information or may be defined as a new field.
Alternatively, a device participating in D2D communication may have
an additional ID solely for D2D communication in addition to ID
used for communication with the eNB and DL assignment information
transmitted (e.g., masked with a corresponding RNTI) for the ID for
D2D communication may be construed as a signal indicating uplink
reception operation. For example, the eNB can transmit DL
assignment information for ID_UE2_cell to UE2 that receives data in
D2D communication.
[0234] As described above, the eNB schedules uplink resources for
D2D communication in the D2D communication scheme proposed by the
present invention, and thus it can be assumed that D2D
communication and normal uplink transmission/reception do not
collide. However, when the eNB instructs a specific UE to perform
reception operation (i.e. D2D data reception operation) through an
uplink resource at a specific time, uplink transmission may be
reserved for the UE at the specific time. In this case, the
reserved uplink transmission can be cancelled. For example, it is
possible to provide higher priority to D2D data reception than
uplink transmission for which transmission time is pre-designated
by higher layer signaling, such as periodic CSI reporting or
periodic SRS transmission. Furthermore, in the case of uplink
transmission operation voluntarily performed by a UE, such as
scheduling request or random access attempt, the uplink
transmission operation may be prevented from being performed when
the UE receives a signal from another UE. That is, when uplink
transmission and D2D data reception (i.e. reception operation
through an uplink resource) collide, uplink transmission can be
dropped.
[0235] 4. D2D Communication Maintenance
[0236] A process for sustaining D2D communication includes an
operation of performing retransmission or new D2D data transmission
using acknowledgement information about data transmitted through a
D2D link, an operation of determining an appropriate transmit
power, MCS level, etc. for the D2D link from feedback for channel
quality of the D2D link, etc. For this process, a device (UE2 in
FIG. 13) that receives D2D data needs to feed back ACK/NACK
information and/or CSI.
[0237] As shown in step S1390 of FIG. 13, UE2 may transmit ACK/NACK
information about D2D transmission and/or CSI on the D2D link to
the eNB instead of to UE1. The ACK/NACK information and/or CSI are
transmitted to the eNB because it is preferable that the eNB
considers feedback information for sustaining D2D communication
since D2D communication scheduling is performed by the eNB although
transmission and reception of D2D data are carried out between
devices. A description will be given of a method for transmitting
ACK/NACK information and CSI with respect to D2D communication.
[0238] 4-1. Transmission of ACK/NACK with Respect to D2D
Communication
[0239] In FIG. 13, UE1 may transmit data to UE2 on the D2D link on
the basis of the scheduling information (S1360) from the eNB and
UE2 may receive the data from UE1 on the D2D link on the basis of
the scheduling information (S1370) from the eNB (S1380). UE2 may
attempt to decode the signal received from UE1 and signal the
decoding result (e.g. whether decoding has been successfully
performed or not) to the eNB (S1390).
[0240] Since UE2 transmits ACK/NACK information to the eNB instead
of UE1, parameters configured to transmit ACK/NACK for a normal
downlink signal from the eNB can be reused as parameters (ACK/NACK
transmit power, scrambling sequence, etc.) for transmitting
ACK/NACK for a signal received through the D2D link and these
parameters may be different from parameters for data transmission
through the D2D link.
[0241] For example, transmit power for signal transmission on the
D2D link can be controlled according to pathloss between devices or
fixed to a specific level in consideration of the fact that the
channel state of the D2D link does not abruptly vary with time
since D2D communication is performed between adjacent devices in
general. Since ACK/NACK information about D2D transmission from UE1
to UE2 needs to be received by the eNB instead of UE1, transmit
power needs to be determined based on pathloss between the eNB and
UE2. For example, UE2 can determine transmit power of ACK/NACK
information about D2D communication according to a transmit power
control (TPC) command which is signaled to UE2 by the eNB for
normal uplink control information transmission rather than D2D
communication.
[0242] In addition, it is necessary to determine an ACK/NACK
resource to enable UE2 to transmit the ACK/NACK information about
D2D communication on uplink. The ACK/NACK resource may be a
resource configured for UE2 through higher layer signaling (e.g.
RRC signaling) or an ACK/NACK resource corresponding to a CCE index
of a PDCCH decoded by UE2. Here, the PDCCH may be a channel on
which the eNB transmits DCI related to normal uplink/downlink
transmission and reception with respect to UE2 or a channel on
which the eNB transmits scheduling information (e.g. scheduling
information in step S1370) for D2D communication to UE2.
[0243] While ACK/NACK information about a D2D signal received by
UE2 may be transmitted alone to the eNB, the ACK/NACK information
may be transmitted through an uplink subframe along with ACK/NACK
information about a downlink signal (e.g. downlink data transmitted
on a PDSCH) received by UE2 from the eNB. To simultaneously
transmit a plurality of ACKs/NACKs, ACK/NACK bundling, channel
selection, joint encoding, etc. may be used. For example, it can be
assumed that UE receives a PDSCH from the eNB in subframe n1 and
receives D2D data from UE1 in subframe n2. In addition, it can be
assumed that two ACK/NACK signals (i.e. ACK/NACK information about
the PDSCH received from the eNB and ACK/NACK information about the
D2D data received from UE1) are transmitted in subframe n3. In this
case, a result of a logical AND operation performed on the two
ACK/NACK signals can be transmitted as final ACK/NACK information
when ACK/NACK bundling is employed. Otherwise, when channel
selection is applied, states of the two ACK/NACK signals can be
represented by previously determining a PUCCH resource index
corresponding to the signal in subframe nl, a PUCCH resource index
corresponding to the signal in subframe n2 and ACK/NACK information
state, selecting one of PUCCH resources and transmitting the
selected PUCCH resource as ACK/NACK information. When joint coding
is used, a result obtained by encoding the two ACK/NACK signals
together can be transmitted using a resource determined in a
predetermined format (e.g. PUCCH format 3).
[0244] When UE2 can transmit ACK/NACK for the PDSCH transmitted
from the eNB and ACK/NACK for the D2D data transmitted from UE1, as
described above, the number of ACK/NACK signals that need to be
processed may be changed according to whether a subframe through
which D2D transmission is performed (or a subframe through which
D2D transmission may be performed) is present or not even if the
number of PDSCHs transmitted from the eNB is fixed. Accordingly,
the number of ACK/NACK signals on which an ACK/NACK logical AND
operation is performed, a rule of mapping ACK/NACK transmission
resources and ACK/NACK information states and/or a coding rate used
for joint encoding (or the number of joint-encoded ACK/NACK bits)
may be changed according to whether or not a D2D transmission
subframe is present. Specifically, when the D2D link is not present
in the above-described example, UE2 can transmit only ACK/NACK
information about the PDSCH transmitted in subframe n1 in subframe
n3. However, when the D2D link is present (or possibility of D2D
link transmission is set by the eNB), UE2 needs to transmit
ACK/NACK information regarding the signals received in subframes n1
and n2 in subframe n3.
[0245] FIG. 14 illustrates exemplary transmission of ACK/NACK
information for D2D transmission according to the present
invention. FIG. 14 assumes a case in which a D2D link is
established on uplink in the case of an FDD system, timing (i.e.
subframe n1) at which a PDSCH is transmitted from the eNB to UE2
corresponds to timing (i.e. subframe n2) at which D2D data is
transmitted from UE1 to UE2, and ACK/NACK signals for the signals
in subframes n1 and n2 are transmitted in subframe n3.
[0246] If a D2D link is not present, as illustrated in FIG. 14(a),
ACK/NACK (or A/N) for transmission on a single DL subframe
(subframe n1) can be transmitted in UL subframe n3(=n1+4).
[0247] In subframe n2 (=n1) in which a D2D link is activated, as
illustrated in FIG. 14(b), UE2 can receive the PDSCH from the eNB
through a DL band and, simultaneously, receive the D2D data from
UE1 through a UL band, and thus ACK/NACK information about a
plurality of subframes (i.e. subframe n1 in which the PDSCH is
transmitted and subframe n2 in which the D2D data is transmitted)
can be transmitted in subframe n3 (=n1+4) after the lapse of 4 ms
from subframe n2.
[0248] FIG. 14(c) illustrates a method of transmitting ACK/NACK
information with respect to transmission through a fixed number of
subframes in a single UL subframe at all times irrespective of
presence or absence of D2D link transmission. In this case,
operation of a UE to transmit ACK/NACK information can be simply
defined. When ACK/NACK information for transmission in a single
subframe is transmitted (FIG. 14(a)) or ACK/NACK information for
transmission in two subframes (FIG. 14(b)) is transmitted based on
presence or absence of a D2D link, a rule for ACK/NACK bundling,
channel selection or joint encoding needs to be additionally
defined, complicating UE operation. However, if only ACK/NACK
information for transmission in a single subframe is transmitted in
UL subframe n3 at all times irrespective of whether D2D link
transmission is performed or not, the rule with respect to ACK/NACK
bundling, channel selection or joint encoding can be used without
change.
[0249] To achieve this, the eNB can prevent scheduling of PDSCH
transmission to UE2 in a DL subframe related to ACK/NACK
transmission in subframe n3 and signal information about the DL
subframe to UE2. For example, the eNB can signal the information in
the form of a bitmap indicating the DL subframe in which PDSCH
transmission is not performed. If D2D link transmission is
performed in subframe n2, as illustrated in FIG. 14(c), the eNB can
determine that PDSCH transmission is not carried out in subframe n1
and signal this to UE2. Accordingly, UE2 can transmit ACK/NACK
information for transmission in a single subframe (i.e. subframe
n2) to the eNB through subframe n3 all the time.
[0250] The principle of the present invention, described through
the above example, can be equally applied to a system that needs to
transmit a plurality of ACKs/NACKs in a single uplink subframe even
when a D2D link is not present since carrier aggregation and/or TDD
is applied. That is, when a UE transmits N ACK/NACK signals for
PDSCH signals received through one or more subframes and/or one or
more carriers (or cells) in a single uplink subframe, if the UE
needs to additionally transmit ACK/NACK information for a D2D link,
the UE can simultaneously transmit the ACK/NACK signals for the
PDSCH signals and the ACK/NACK signal for the D2D link using the
above-described method. Specifically, the UE can transmit N+1
ACK/NACK signals corresponding to the sum of the ACK/NACK signals
for the PDSCH signals and the ACK/NACK signal for the D2D link
through ACK/NACK bundling, channel selection or joint encoding. In
addition, the UE can transmit a maximum of N ACK/NACK signals in a
corresponding uplink subframe by limiting PDSCH signal transmission
(e.g. limiting the number of ACK/NACK signals to less than N-1 when
the D2D link is activated and thus ACK/NACK for the D2D link needs
to be transmitted).
[0251] A time when ACK/NACK information for a signal received
through the D2D link is transmitted may be determined by one of the
following methods.
[0252] Method 1) When a PDSCH is transmitted from an eNB in a DL
subframe corresponding to subframe n, ACK/NACK information for a
D2D signal received in subframe n can be transmitted in a subframe
scheduled to transmit ACK/NACK information for the PDSCH. For
example, k=8 since a UL HARQ process has a period of 8 ms in an LTE
FDD system.
[0253] Method 2) ACK/NACK information for a D2D signal received in
subframe n may be transmitted in subframe n+m. Here, m can be
determined as a minimum integer that makes subframe n+m correspond
to a UL subframe, from among integers equal to or greater than a
predetermined value (e.g. 4 ms which is a unit processing time in
3GPP LTE) to ensure decoding time for the received signal.
[0254] Method 3) ACK/NACK information for a signal received in
subframe n may be transmitted in subframe n+m while piggybacking on
a PUSCH transmitted from UE2. Here, m can be determined as a
minimum integer that makes subframe n+m correspond to a UL subframe
scheduled to transmit the PUSCH, from among integers equal to or
greater than a predetermined value (e.g. 4 ms which is a basic
processing time in 3GPP LTE) to ensure decoding time for the
received signal.
[0255] 4-2. CSI Transmission with Respect to D2D Link
[0256] The following description is applicable to D2D link
detection result reporting in step S1350 of FIG. 13 and/or
reporting of CSI about the D2D link in step S1390 of FIG. 13.
[0257] A device (e.g. UE2 of FIG. 13) that receives D2D data from a
device (e.g. UE1 of FIG. 13) that transmits the D2D data on a D2D
link can report channel state information (CSI) about the D2D link
to the eNB for transmit power control and MCS in order to control
transmit power of D2D data transmission and select an MCS to be
applied to D2D data transmission. The eNB can determine parameters
to be applied to D2D data transmission in consideration of the CSI
received from UE2 and provide scheduling information for D2D
transmission to UE1 and/or UE2. Accordingly, UE1 can transmit data
to UE2 according to the scheduling information determined by the
eNB on the basis of feedback from UE2.
[0258] The eNB can transmit a CSI report request to UE2 for
feedback of the CSI about the D2D link. While the CSI report
request in conventional eNB-to-UE communication is a control signal
for triggering reporting of CSI on a downlink resource by a UE, the
CSI report request with respect to the D2D link in the present
invention can be defined as a control signal for triggering
reporting of CSI on an uplink resource from UE1 to UE2. That is,
while CSI is calculated on the assumption that downlink
transmission is performed at a specific time and/or in a specific
frequency resource (which may be called a CSI reference resource)
in a legacy system, UE2 can determine an uplink resource as a CSI
reference resource and calculate/determine CSI based on uplink
transmission of UE1 in the CSI reference resource in the present
invention. Specifically, UE2 can calculate/determine CSI about a
corresponding uplink resource on the basis of a UL DMRS, SRS or
PRACH preamble transmitted on the corresponding uplink resource
from UE1.
[0259] FIG. 15 illustrates an example of determining a CSI
reference resource according to the present invention. As shown in
FIG. 15, a CSI reference resource for calculating CSI in subframe n
can be determined as subframe n-k. Subframe n-k can be set to an
uplink resource and k can be determined by one of the following
methods.
[0260] Method 1) k may be set to an integer that makes subframe n-k
correspond to a latest UL subframe belonging to the same UL HARQ
process as the UL HARQ process to which subframe n belongs. In this
case, it can be assumed that channel environments (e.g.
interference applied to an uplink resource) are similar in the same
UL HARQ process.
[0261] Method 2) k may be set to a minimum integer from among
integers that make subframe n-k become a UL subframe corresponding
to or after a DL subframe in which a CSI report request for
triggering a CSI report in subframe n is received on the basis of
the DL subframe. Simultaneously, k can be determined as a
predetermined minimum value (e.g. 4 ms which is the unit processing
time in 3GPP LTE) in order to ensure CSI calculation time. In this
case, since the CSI reference resource is present when the CSI
report request is received or after the CSI report request
reception time, UE2 calculates CSI using the CSI reference resource
after receiving the CSI report request. Accordingly, unnecessary
CSI calculation can be omitted. That is, it is possible to
eliminate calculation of CSI about a resource present prior to
reception of the CSI report request when the CSI reference resource
is determined as a resource prior to the CSI report request
reception time.
[0262] Method 3) k may be set to a minimum integer that makes
subframe n-k correspond to a UL subframe. Simultaneously, k may be
set to a value greater than a predetermined minimum value (e.g. 4
ms which is the unit process time in 3GPP LTE) to ensure CSI
calculation time. Here, subframe n-k may be a UL subframe
corresponding to or prior to a DL subframe in which the CSI report
request is received. In this case, a valid CSI reference resource
can be set even when a period between the CSI report request
reception time and CSI reporting time is insufficient. That is, a
valid CSI reference resource does not exist when a UL subframe that
ensures CSI calculation time is not present between a subframe in
which the CSI report request is received and a subframe in which
CSI is reported in the case of method 2, whereas the valid CSI
reference resource can be configured at all times in the case of
method 3.
[0263] Method 4) k may be set to a minimum integer that makes
subframe n-k correspond to a subframe scheduled to transmit a
specific signal of UE1, that is, a signal (e.g. a UL DMRS, SRS or
PRACH preamble transmitted by UE1) used for CSI calculation by UE2.
Simultaneously, k may be set to a value greater than a
predetermined minimum value (e.g. 4 ms which is the unit processing
time in 3GPP LTE) to ensure CSI calculation time. In this case, the
CSI reference resource can be defined as a resource including a
specific signal (e.g. UL DMRS, SRS or PRACH) of UE1 all the
time.
[0264] To determine an uplink resource as a CSI reference resource
and perform CSI feedback for D2D communication as described above,
determination of the CSI reference resource and CSI feedback need
to be signaled to a device that performs CSI feedback through
higher layer signaling. For example, if a specific UE (e.g. UE2)
can receive a signal from another UE (e.g. UE1) through an uplink
resource (or a transmission mode in which the specific UE can
receive a signal from the other UE is set), a UL subframe also
needs to be considered as a valid CSI reference resource and the
eNB can transmit a higher layer signal indicating that the UL
subframe is set to a valid CSI reference resource to the specific
UE.
[0265] To regard the UL subframe as the valid CSI reference
resource, UE2 needs to measure interference in the UL subframe (on
the assumption that a channel from UE1 can be estimated through a
signal such as an SRS, CSI-RS, etc.). CSI calculation in a normal
DL subframe (that is, CSI calculation with respect to DL
transmission) is performed according to interference measurement
that considers a signal, which is left after a CRS from a serving
cell is canceled, as interference. However, a new interference
measurement resource for CSI measurement in a UL resource is needed
because a CRS is not present in a UL subframe.
[0266] Accordingly, the eNB can signal a resource element (RE) to
be used for interference measurement to a UE through higher layer
signaling. The RE used for interference measurement in a UL
resource may be an RE on which an SRS is transmitted in the uplink
resource. In this case, the eNB can signal a specific SRS of UE1 to
UE2 and enable UE2 to use an RE on which the specific SRS of UE1 is
transmitted for interference measurement.
[0267] The SRS may be a null SRS or zero transmission power SRS and
can be used for interference measurement only. In this case, UE2
can directly measure an RE on which the null SRS or zero
transmission power SRS is transmitted to measure interference.
[0268] Otherwise, the SRS may be an SRS transmitted by a specific
UE (e.g. UE1). In this case, UE2 can measure a signal left after
the SRS transmitted on an SRS transmission RE is canceled as
interference. Here, UE2 may also estimate a channel from UE1 using
the SRS.
[0269] While UE2 calculates CSI about the D2D link using the SRS
from UE1 (or measures received signal strength or interference) in
the above-described example, the present invention is not limited
thereto and UE2 may measure the CSI about the D2D link using a
specific signal (e.g. a UL DMRS or PRACH) transmitted by UE1 and
known to both UE1 and UE2.
[0270] Transmit power from UE1 is different form transmit power
from the eNB from the viewpoint of UE2. Even if a device operating
as an eNB instantaneously performs operation of UE1 to transmit a
signal to UE2 using a UL resource, this transmission is performed
using the UL resource and thus transmit power different from
transmit power of transmission carried out using a DL resource is
used for transmission. This transmit power difference affects CSI
calculation by UE2. Accordingly, the eNB can signal to UE2 a
transmit power used by UE1 for transmission using a specific UL
resource. Particularly, when the eNB performs operation of UE1, the
eNB can inform UE2 of the transmit power of the D2D link by
signaling a transmit power difference between a UL resource and a
DL resource.
[0271] While D2D communication is performed in such a manner that
UE1 performs normal uplink transmission (e.g. transmission of a
PUCCH, PUSCH, SRS, UL DMRS, PRACH preamble, etc.) and UE2 receives
a signal transmitted on uplink from another UE through an uplink
resource, distinguished from legacy wireless communication systems,
in the above-mentioned examples, the present invention is not
limited thereto. That is, the present invention involves D2D
communication performed in such a manner that UE1 performs downlink
transmission (e.g. transmission of a PDCCH, PDSCH, CRS, CSI-RS,
etc.), distinguished from legacy wireless communication systems,
and UE2 receives a signal transmitted on downlink from another UE.
In any case, D2D communication can be performed through an uplink
resource of legacy wireless communication systems.
[0272] For example, when UE1 performs downlink transmission, UE2
can regard UE1 as a device corresponding to part of antenna ports
of the eNB. That is, UE2 can be linked to the eNB to receive
control information from the eNB and receive data from part (UE1)
of the antenna ports of the eNB. Accordingly, UE2 can perform the
same operation as operation of receiving downlink data from the
eNB, which is transmitted on a time-frequency resource (which may
be an uplink resource in legacy wireless communication systems)
scheduled by the eNB, in the legacy wireless communication
systems.
[0273] For the above-mentioned operation, the eNB can allocate a
CRS or CSI-RS antenna port to UE1 through higher layer signaling
and UE2 can measure CSI about the D2D link using a CRS or CSI-RS
from UE1.
[0274] When D2D transmission of UE1 is performed on an uplink
resource, the CRS or CSI-RS may be irregularly transmitted from
UE1. This is because an uplink resource allocated to UE1 for D2D
communication needs to be dynamically controlled according to
traffic of UE1 since static allocation of a specific uplink
resource to a specific UE may decrease network throughput.
Accordingly, when UE1 transmits some or all CRS or CSI-RS on an
uplink resource, it is necessary to dynamically signal presence or
absence of the CRS or CSI-RS in the uplink resource to UE2.
[0275] For example, the eNB can embed an indicator indicating
whether an RS is present or not in a specific resource in control
information transmitted to UE2 through a physical layer control
channel (e.g. PDCCH). While the RS is a CRS or CSI-RS transmitted
from UE1, UE2 may recognize the RS as an RS from a specific antenna
port of the eNB. Otherwise, when the eNB requests UE2 to feed back
CSI (CSI on the D2D link from UE1) on a specific antenna port, UE2
can consider that an RS (CRS or CSI-RS) for CSI feedback is
transmitted. When a CSI report request from the eNB is not present,
UE2 can consider that an RS for the CSI report request is not
transmitted. In any case, UE2 needs to measure the CSI on the D2D
link from UE1 on the basis of an irregularly transmitted RS and
thus it is necessary to newly define a CSI reference resource for
CSI measurement.
[0276] For example, when CSI about downlink transmission (downlink
transmission from UE1) through a specific antenna port needs to be
reported in a specific uplink resource since the eNB transmits the
CSI report request to UE2, an uplink resource in which downlink
transmission (downlink transmission from UE1) through the specific
antenna port is performed, which is scheduled when the CSI report
request is transmitted, may be set to a CSI reference resource.
Furthermore, when CSI on the D2D link, which is reported in
subframe n, is calculated using subframe n-k as a CSI reference
resource, k may be set to a minimum value from among values that
make subframe n-k correspond to a subframe in which an RS (e.g. CRS
or CSI-RS) from UE1 is transmitted and, at the same time, to a
value greater than a predetermined minimum value (e.g. 4 ms which
is the unit processing time in 3GPP LTE) to ensure CSI calculation
time of UE2.
[0277] In D2D communication according to the present invention, the
above-described embodiments can be independently applied or two or
more thereof can be simultaneously applied and description of
redundant parts is omitted for clarity.
[0278] FIG. 16 illustrates configuration of transceivers according
to the present invention.
[0279] Referring to FIG. 16, a first transceiver 1610 according to
the present invention may include a reception module 1611, a
transmission module 1612, a processor 1613, a memory 1614 and a
plurality of antennas 1615. The antennas 1615 refer to transceivers
supporting MIMO transmission and reception. The reception module
1611 may receive signals, data and information from another device
and/or an eNB. The transmission module 1612 may transmit signals,
data and information to the other device and/or the eNB. The
processor 1613 may control the overall operation of the first
transceiver 1610.
[0280] The first transceiver may be configured to transmit a signal
to another device (e.g. second transceiver). The processor 1613 of
the first transceiver may be configured to request the eNB to
allocate a resource for signal transmission to the second
transceiver. In addition, the processor 1613 may be configured to
receive scheduling information for signal transmission to the
second transceiver from the eNB. Furthermore, the processor 1613
may be configured to transmit a signal to the second transceiver
based on the received scheduling information. Here, the scheduling
information may include information about an uplink resource for
signal transmission from the first transceiver to the second
transceiver.
[0281] The processor 1613 of the first transceiver may be
configured to transmit a signal for channel state measurement in
the second transceiver to the second transceiver. In addition, the
first transceiver may perform transmission on the uplink resource
according to a downlink channel/signal format. Otherwise, the first
transceiver may perform transmission on the uplink resource
according to an uplink channel/signal format.
[0282] In addition, the processor 1613 of the first transceiver
1610 may process information received by the first transceiver,
information to be transmitted by the first transceiver, etc. and
the memory 1614 may store the processed information for a
predetermined time and may be replaced by a component such as a
buffer (not shown).
[0283] A second transceiver 1620 according to the present invention
may include a reception module 1621, a transmission module 1622, a
processor 1623, a memory 1624 and a plurality of antennas 1625. The
antennas 1625 refer to transceivers supporting MIMI transmission
and reception. The reception module 1621 may receive signals, data
and information from the eNB and/or another device. The
transmission module 1622 may transmit signals, data and information
to the eNB and/or the other device. The processor 1623 may control
overall operation of the second transceiver 1620.
[0284] The second transceiver may be configured to receive a signal
from another device (e.g. first transceiver). The processor 1623 of
the second transceiver may be configured to receive, from the eNB,
scheduling information about signal transmission from the first
transceiver to the second transceiver. In addition, the processor
1623 may be configured to receive a signal from the first
transceiver based on the received scheduling information. Here, the
scheduling information may include information on an uplink
resource used for the second transceiver to receive the signal from
the first transceiver.
[0285] The processor 1623 of the second transceiver may be
configured to transmit ACK/NACK information for a signal received
from the first transceiver alone or along with ACK/NACK information
for a signal received from the eNB to the eNB. Here, the second
transceiver can transmit ACK/NACK information for a maximum of N
received signals in a single uplink subframe. N can be set to a
fixed value irrespective of whether a signal is received from the
first transceiver or not. ACK/NACK information transmission time
may be determined by one of the methods described in above
embodiments of the present invention.
[0286] The processor 1623 of the second transceiver may be
configured to receive a signal for channel state measurement from
the first transceiver. Furthermore, the processor 1623 of the
second transceiver may be configured to transmit measured CSI to
the eNB. Here, a reference resource applied to CSI calculation can
be determined by one of the methods described in the above
embodiments.
[0287] When uplink transmission of the second transceiver is set in
the uplink resource scheduled to receive a signal from the first
transceiver, uplink transmission of the second transceiver may be
dropped.
[0288] In addition, the processor 1623 of the second transceiver
1620 may process information received by the second transceiver
1620, information to be transmitted by the second transceiver 1620,
etc. and the memory 1624 may store the processed information for a
predetermined time and may be replaced by a component such as a
buffer (not shown).
[0289] The first and second transceivers may transmit/receive
signals to/from an eNB device (not shown). The eNB device may be
configured to manage signal transmission from the first transceiver
to the second transceiver. In addition, the eNB device may include
a transmission module transmitting signals to the first and second
transceivers, a reception module receiving signals from the first
and second transceivers and a processor.
[0290] The processor of the eNB device may be configured to
receive, from the first transceiver, a resource allocation request
for signal transmission from the first transceiver to the second
transceiver and to transmit, to the first and second transceivers,
scheduling information for signal transmission from the first
transceiver to the second transceiver. The scheduling information
determined by the eNB device may include information on an uplink
resource through which the first transceiver transmits a signal to
the second transceiver.
[0291] The configurations of the eNB device and the transceivers
may be implemented such that the above-described embodiments can be
independently applied or two or more thereof can be simultaneously
applied and description of redundant parts is omitted for
clarity.
[0292] Description of the eNB device in FIG. 16 may be equally
applied to a relay as a downlink transmitter or an uplink receiver
and description of the transceiver may be equally applied to a UE
or a relay as a downlink receiver or an uplink transmitter.
[0293] The embodiments of the present invention may be achieved by
various means, for example, hardware, firmware, software, or a
combination thereof.
[0294] In a hardware configuration, the methods according to the
embodiments of the present invention may be achieved by one or more
Application Specific Integrated Circuits (ASICs), Digital Signal
Processors (DSPs), Digital Signal Processing Devices (DSPDs),
Programmable Logic Devices (PLDs), Field Programmable Gate Arrays
(FPGAs), processors, controllers, microcontrollers,
microprocessors, etc.
[0295] In a firmware or software configuration, the embodiments of
the present invention may be implemented in the form of a module, a
procedure, a function, etc. For example, software code may be
stored in a memory unit and executed by a processor. The memory
unit is located at the interior or exterior of the processor and
may transmit and receive data to and from the processor via various
known means.
[0296] The embodiments of the present invention described
hereinbelow are combinations of elements and features of the
present invention. The elements or features may be considered
selective unless otherwise mentioned. Each element or feature may
be practiced without being combined with other elements or
features. Further, an embodiment of the present invention may be
constructed by combining parts of the elements and/or features.
Operation orders described in embodiments of the present invention
may be rearranged. Some constructions of any one embodiment may be
included in another embodiment and may be replaced with
corresponding constructions of another embodiment. It will be
obvious to those skilled in the art that claims that are not
explicitly cited in each other in the appended claims may be
presented in combination as an embodiment of the present invention
or included as a new claim by subsequent amendment after the
application is filed.
[0297] Those skilled in the art will appreciate that the present
invention may be carried out in other specific ways than those set
forth herein without departing from the spirit and essential
characteristics of the present invention. The above embodiments are
therefore to be construed in all aspects as illustrative and not
restrictive. The scope of the invention should be determined by the
appended claims and their legal equivalents, not by the above
description, and all changes coming within the meaning and
equivalency range of the appended claims are intended to be
embraced therein.
INDUSTRIAL APPLICABILITY
[0298] The above-described embodiments of the present invention can
be applied to various mobile communication systems.
* * * * *